diff --git a/CHANGELOG.md b/CHANGELOG.md
index bb10362..db4664c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - GeoJSON to JSON:
   - Include name in organisation and phase references
   - Process funders/organisations in phases correctly, including spotting inconsistent funders/organisations
+  - Report on inconsistent networks
 
 ## [0.4.0] - 2022-11-09
 
diff --git a/libcoveofds/geojson.py b/libcoveofds/geojson.py
index 3afe126..4610b7a 100644
--- a/libcoveofds/geojson.py
+++ b/libcoveofds/geojson.py
@@ -200,6 +200,7 @@ def __init__(self):
         self._inconsistent_organisation_ids_by_network_id: defaultdict = defaultdict(
             set
         )
+        self._inconsistent_network_ids_seen: set = set()
 
     def process_data(self, nodes_data: dict, spans_data: dict) -> None:
         """Process data. Results are stored on object to get with other methods."""
@@ -223,32 +224,86 @@ def _process_network(self, geojson_feature_node_or_span: dict) -> None:
             and "network" in geojson_feature_node_or_span["properties"]
         ):
             network = geojson_feature_node_or_span["properties"]["network"]
-            if network.get("id"):
-                # TODO check for inconsistent data here!
-                self._networks[network.get("id")] = copy.deepcopy(network)
-                self._networks[network.get("id")]["nodes"] = []
-                self._networks[network.get("id")]["spans"] = []
-                self._networks[network.get("id")]["phases"] = {}
-                self._networks[network.get("id")]["organisations"] = {}
-
-                # Sort references to phases in contracts
-                if "contracts" in self._networks[network.get("id")] and isinstance(
-                    self._networks[network.get("id")]["contracts"], list
-                ):
-                    for contract in self._networks[network.get("id")]["contracts"]:
-                        if "relatedPhases" in contract and isinstance(
-                            contract["relatedPhases"], list
+            if isinstance(network, dict):
+                network_id = network.get("id")
+                if isinstance(network_id, str) and network_id:
+
+                    # TODO nodes/spans/phases/organisations should not be set in network - check this and warn if so
+
+                    # Is data already seen?
+                    if network_id in self._networks:
+                        # Is it inconsistent with what we have seen before?
+                        if json_diff_function(
+                            self._networks[network_id]["network_data_original"], network
+                        ):
+                            # record error for later
+                            self._inconsistent_network_ids_seen.add(network_id)
+
+                            # Check references to phases in contracts are consistent with what we have seen before.
+                            # This will give a more specific error on the phase_id.
+                            # (However, 2 errors will be recorded - one for network_id and one for phrase_id!
+                            #  Can we make that tidier?
+                            #  Suspect as we work to make errors more informative that will happen anyway #TODO)
+                            if "contracts" in self._networks[network_id][
+                                "network_data_output"
+                            ] and isinstance(
+                                self._networks[network_id]["network_data_output"][
+                                    "contracts"
+                                ],
+                                list,
+                            ):
+                                for contract in self._networks[network_id][
+                                    "network_data_output"
+                                ]["contracts"]:
+                                    if "relatedPhases" in contract and isinstance(
+                                        contract["relatedPhases"], list
+                                    ):
+                                        for phase_reference in contract[
+                                            "relatedPhases"
+                                        ]:
+                                            self._process_phase(
+                                                network_id, phase_reference
+                                            )
+                    else:
+
+                        # Not seen this before!
+
+                        # Store it
+                        self._networks[network_id] = {
+                            "network_data_original": copy.deepcopy(network),
+                            "network_data_output": copy.deepcopy(network),
+                            "nodes": [],
+                            "spans": [],
+                            "phases": {},
+                            "organisations": {},
+                        }
+
+                        # Sort references to phases in contracts
+                        # (Must do after storing, as this writes data to the stored network)
+                        if "contracts" in self._networks[network_id][
+                            "network_data_output"
+                        ] and isinstance(
+                            self._networks[network_id]["network_data_output"][
+                                "contracts"
+                            ],
+                            list,
                         ):
-                            out: list = []
-                            for phase_reference in contract["relatedPhases"]:
-                                phase_data = self._process_phase(
-                                    network.get("id"), phase_reference
-                                )
-                                if phase_data:
-                                    out.append(phase_data)
-                                else:
-                                    out.append(phase_reference)
-                            contract["relatedPhases"] = out
+                            for contract in self._networks[network_id][
+                                "network_data_output"
+                            ]["contracts"]:
+                                if "relatedPhases" in contract and isinstance(
+                                    contract["relatedPhases"], list
+                                ):
+                                    out: list = []
+                                    for phase_reference in contract["relatedPhases"]:
+                                        phase_data = self._process_phase(
+                                            network_id, phase_reference
+                                        )
+                                        if phase_data:
+                                            out.append(phase_data)
+                                        else:
+                                            out.append(phase_reference)
+                                    contract["relatedPhases"] = out
 
     def _process_node(self, geojson_feature_node: dict) -> None:
         node = copy.deepcopy(geojson_feature_node.get("properties", {}))
@@ -380,16 +435,17 @@ def get_json(self) -> dict:
         out: dict = {"networks": []}
         for network in self._networks.values():
             # We are going to change network, so we need to take a copy
-            network = copy.deepcopy(network)
-            # Arrays have minItems: 1 set - so if no content, remove the empty array
-            for key in ["nodes", "spans", "phases", "organisations", "contracts"]:
-                if key in network and not network[key]:
-                    del network[key]
-            # Sometimes we store these things in dicts - turn to lists
+            network_data = copy.deepcopy(network["network_data_output"])
+            # Copy other data we have built to network_data
+            # Arrays have minItems: 1 set - so only add if we actually have content
+            for key in ["nodes", "spans"]:
+                if network[key]:
+                    network_data[key] = network[key]
             for key in ["phases", "organisations"]:
-                if key in network:
-                    network[key] = list(network[key].values())
-            out["networks"].append(network)
+                if network[key]:
+                    network_data[key] = list(network[key].values())
+            # build return
+            out["networks"].append(network_data)
         return out
 
     def get_meta_json(self) -> dict:
@@ -410,5 +466,6 @@ def get_meta_json(self) -> dict:
             k: {"organisation_ids": sorted(list(v))}
             for k, v in self._inconsistent_organisation_ids_by_network_id.items()
         }
+        out["inconsistent_network_ids"] = list(self._inconsistent_network_ids_seen)
         # return
         return out
diff --git a/make_expected_test_data.sh b/make_expected_test_data.sh
index 6e59619..e72e0e0 100755
--- a/make_expected_test_data.sh
+++ b/make_expected_test_data.sh
@@ -19,6 +19,7 @@ libcoveofds gjtoj --outputmetafilename tests/fixtures/geojson_to_json/organisati
 libcoveofds gjtoj --outputmetafilename tests/fixtures/geojson_to_json/phase_funders_1.meta.expected.json  tests/fixtures/geojson_to_json/phase_funders_1.nodes.geo.json tests/fixtures/geojson_to_json/phase_funders_1.spans.geo.json  tests/fixtures/geojson_to_json/phase_funders_1.expected.json
 libcoveofds gjtoj --outputmetafilename tests/fixtures/geojson_to_json/phases_inconsistent_1.meta.expected.json  tests/fixtures/geojson_to_json/phases_inconsistent_1.nodes.geo.json tests/fixtures/geojson_to_json/phases_inconsistent_1.spans.geo.json  tests/fixtures/geojson_to_json/phases_inconsistent_1.expected.json
 libcoveofds gjtoj --outputmetafilename tests/fixtures/geojson_to_json/organisations_inconsistent_1.meta.expected.json  tests/fixtures/geojson_to_json/organisations_inconsistent_1.nodes.geo.json tests/fixtures/geojson_to_json/organisations_inconsistent_1.spans.geo.json  tests/fixtures/geojson_to_json/organisations_inconsistent_1.expected.json
+libcoveofds gjtoj --outputmetafilename tests/fixtures/geojson_to_json/network_inconsistent_1.meta.expected.json  tests/fixtures/geojson_to_json/network_inconsistent_1.nodes.geo.json tests/fixtures/geojson_to_json/network_inconsistent_1.spans.geo.json  tests/fixtures/geojson_to_json/network_inconsistent_1.expected.json
 
 # JSON to GeoJSON
 libcoveofds jtogj --outputmetafilename tests/fixtures/json_to_geojson/basic_1.expected.meta.json tests/fixtures/json_to_geojson/basic_1.json tests/fixtures/json_to_geojson/basic_1.expected.nodes.geo.json tests/fixtures/json_to_geojson/basic_1.expected.spans.geo.json
diff --git a/tests/fixtures/geojson_to_json/basic_1.meta.expected.json b/tests/fixtures/geojson_to_json/basic_1.meta.expected.json
index 0357490..5fc29c6 100644
--- a/tests/fixtures/geojson_to_json/basic_1.meta.expected.json
+++ b/tests/fixtures/geojson_to_json/basic_1.meta.expected.json
@@ -56,5 +56,6 @@
         }
     },
     "inconsistent_phases_by_network_id": {},
-    "inconsistent_organisations_by_network_id": {}
+    "inconsistent_organisations_by_network_id": {},
+    "inconsistent_network_ids": []
 }
\ No newline at end of file
diff --git a/tests/fixtures/geojson_to_json/network_inconsistent_1.expected.json b/tests/fixtures/geojson_to_json/network_inconsistent_1.expected.json
new file mode 100644
index 0000000..85d4d71
--- /dev/null
+++ b/tests/fixtures/geojson_to_json/network_inconsistent_1.expected.json
@@ -0,0 +1,98 @@
+{
+    "networks": [
+        {
+            "id": "a096d627-72e1-4f9b-b129-951b1737bff4",
+            "name": "Ghana Fibre Network",
+            "nodes": [
+                {
+                    "id": "1",
+                    "name": "Accra",
+                    "location": {
+                        "type": "Point",
+                        "coordinates": [
+                            -0.174,
+                            5.625
+                        ]
+                    }
+                },
+                {
+                    "id": "2",
+                    "name": "Kumasi",
+                    "status": "operational",
+                    "location": {
+                        "type": "Point",
+                        "coordinates": [
+                            -1.628,
+                            6.711
+                        ]
+                    }
+                }
+            ],
+            "spans": [
+                {
+                    "id": "1",
+                    "name": "Accra to Kumasi",
+                    "start": "1",
+                    "end": "2",
+                    "route": {
+                        "type": "LineString",
+                        "coordinates": [
+                            [
+                                -0.173,
+                                5.626
+                            ],
+                            [
+                                -0.178,
+                                5.807
+                            ],
+                            [
+                                -0.112,
+                                5.971
+                            ],
+                            [
+                                -0.211,
+                                5.963
+                            ],
+                            [
+                                -0.321,
+                                6.17
+                            ],
+                            [
+                                -0.488,
+                                6.29
+                            ],
+                            [
+                                -0.56,
+                                6.421
+                            ],
+                            [
+                                -0.752,
+                                6.533
+                            ],
+                            [
+                                -0.867,
+                                6.607
+                            ],
+                            [
+                                -1.101,
+                                6.585
+                            ],
+                            [
+                                -1.304,
+                                6.623
+                            ],
+                            [
+                                -1.461,
+                                6.727
+                            ],
+                            [
+                                -1.628,
+                                6.713
+                            ]
+                        ]
+                    }
+                }
+            ]
+        }
+    ]
+}
\ No newline at end of file
diff --git a/tests/fixtures/geojson_to_json/network_inconsistent_1.meta.expected.json b/tests/fixtures/geojson_to_json/network_inconsistent_1.meta.expected.json
new file mode 100644
index 0000000..355a899
--- /dev/null
+++ b/tests/fixtures/geojson_to_json/network_inconsistent_1.meta.expected.json
@@ -0,0 +1,63 @@
+{
+    "output_field_coverage": {
+        "/networks": {
+            "count": 1
+        },
+        "/networks/id": {
+            "count": 1
+        },
+        "/networks/name": {
+            "count": 1
+        },
+        "/networks/nodes": {
+            "count": 1
+        },
+        "/networks/nodes/id": {
+            "count": 2
+        },
+        "/networks/nodes/name": {
+            "count": 2
+        },
+        "/networks/nodes/location": {
+            "count": 2
+        },
+        "/networks/nodes/location/type": {
+            "count": 2
+        },
+        "/networks/nodes/location/coordinates": {
+            "count": 2
+        },
+        "/networks/nodes/status": {
+            "count": 1
+        },
+        "/networks/spans": {
+            "count": 1
+        },
+        "/networks/spans/id": {
+            "count": 1
+        },
+        "/networks/spans/name": {
+            "count": 1
+        },
+        "/networks/spans/start": {
+            "count": 1
+        },
+        "/networks/spans/end": {
+            "count": 1
+        },
+        "/networks/spans/route": {
+            "count": 1
+        },
+        "/networks/spans/route/type": {
+            "count": 1
+        },
+        "/networks/spans/route/coordinates": {
+            "count": 1
+        }
+    },
+    "inconsistent_phases_by_network_id": {},
+    "inconsistent_organisations_by_network_id": {},
+    "inconsistent_network_ids": [
+        "a096d627-72e1-4f9b-b129-951b1737bff4"
+    ]
+}
\ No newline at end of file
diff --git a/tests/fixtures/geojson_to_json/network_inconsistent_1.nodes.geo.json b/tests/fixtures/geojson_to_json/network_inconsistent_1.nodes.geo.json
new file mode 100644
index 0000000..d2cd7ce
--- /dev/null
+++ b/tests/fixtures/geojson_to_json/network_inconsistent_1.nodes.geo.json
@@ -0,0 +1,42 @@
+{
+    "type": "FeatureCollection",
+    "features": [
+        {
+            "type": "Feature",
+            "geometry": {
+                "type": "Point",
+                "coordinates": [
+                    -0.174,
+                    5.625
+                ]
+            },
+            "properties": {
+                "id": "1",
+                "name": "Accra",
+                "network": {
+                    "id": "a096d627-72e1-4f9b-b129-951b1737bff4",
+                    "name": "Ghana Fibre Network"
+                }
+            }
+        },
+        {
+            "type": "Feature",
+            "geometry": {
+                "type": "Point",
+                "coordinates": [
+                    -1.628,
+                    6.711
+                ]
+            },
+            "properties": {
+                "id": "2",
+                "name": "Kumasi",
+                "status": "operational",
+                "network": {
+                    "id": "a096d627-72e1-4f9b-b129-951b1737bff4",
+                    "name": "Ghana Fibre Network"
+                }
+            }
+        }
+    ]
+}
\ No newline at end of file
diff --git a/tests/fixtures/geojson_to_json/network_inconsistent_1.spans.geo.json b/tests/fixtures/geojson_to_json/network_inconsistent_1.spans.geo.json
new file mode 100644
index 0000000..da8fca6
--- /dev/null
+++ b/tests/fixtures/geojson_to_json/network_inconsistent_1.spans.geo.json
@@ -0,0 +1,96 @@
+{
+    "type": "FeatureCollection",
+    "features": [
+        {
+            "type": "Feature",
+            "geometry": {
+                "type": "LineString",
+                "coordinates": [
+                    [
+                        -0.173,
+                        5.626
+                    ],
+                    [
+                        -0.178,
+                        5.807
+                    ],
+                    [
+                        -0.112,
+                        5.971
+                    ],
+                    [
+                        -0.211,
+                        5.963
+                    ],
+                    [
+                        -0.321,
+                        6.17
+                    ],
+                    [
+                        -0.488,
+                        6.29
+                    ],
+                    [
+                        -0.56,
+                        6.421
+                    ],
+                    [
+                        -0.752,
+                        6.533
+                    ],
+                    [
+                        -0.867,
+                        6.607
+                    ],
+                    [
+                        -1.101,
+                        6.585
+                    ],
+                    [
+                        -1.304,
+                        6.623
+                    ],
+                    [
+                        -1.461,
+                        6.727
+                    ],
+                    [
+                        -1.628,
+                        6.713
+                    ]
+                ]
+            },
+            "properties": {
+                "id": "1",
+                "name": "Accra to Kumasi",
+                "start": {
+                    "id": "1",
+                    "name": "Accra",
+                    "location": {
+                        "type": "Point",
+                        "coordinates": [
+                            -0.174,
+                            5.625
+                        ]
+                    }
+                },
+                "end": {
+                    "id": "2",
+                    "name": "Kumasi",
+                    "status": "operational",
+                    "location": {
+                        "type": "Point",
+                        "coordinates": [
+                            -1.628,
+                            6.711
+                        ]
+                    }
+                },
+                "network": {
+                    "id": "a096d627-72e1-4f9b-b129-951b1737bff4",
+                    "name": "Ghana Network of Fibre"
+                }
+            }
+        }
+    ]
+}
\ No newline at end of file
diff --git a/tests/fixtures/geojson_to_json/no_geometry_1.meta.expected.json b/tests/fixtures/geojson_to_json/no_geometry_1.meta.expected.json
index a035f61..8afcacd 100644
--- a/tests/fixtures/geojson_to_json/no_geometry_1.meta.expected.json
+++ b/tests/fixtures/geojson_to_json/no_geometry_1.meta.expected.json
@@ -38,5 +38,6 @@
         }
     },
     "inconsistent_phases_by_network_id": {},
-    "inconsistent_organisations_by_network_id": {}
+    "inconsistent_organisations_by_network_id": {},
+    "inconsistent_network_ids": []
 }
\ No newline at end of file
diff --git a/tests/fixtures/geojson_to_json/organisations_1.meta.expected.json b/tests/fixtures/geojson_to_json/organisations_1.meta.expected.json
index 5a3514a..ef2d147 100644
--- a/tests/fixtures/geojson_to_json/organisations_1.meta.expected.json
+++ b/tests/fixtures/geojson_to_json/organisations_1.meta.expected.json
@@ -104,5 +104,6 @@
         }
     },
     "inconsistent_phases_by_network_id": {},
-    "inconsistent_organisations_by_network_id": {}
+    "inconsistent_organisations_by_network_id": {},
+    "inconsistent_network_ids": []
 }
\ No newline at end of file
diff --git a/tests/fixtures/geojson_to_json/organisations_inconsistent_1.meta.expected.json b/tests/fixtures/geojson_to_json/organisations_inconsistent_1.meta.expected.json
index 718f550..a58a145 100644
--- a/tests/fixtures/geojson_to_json/organisations_inconsistent_1.meta.expected.json
+++ b/tests/fixtures/geojson_to_json/organisations_inconsistent_1.meta.expected.json
@@ -148,5 +148,6 @@
                 "GH-RGD-CS333333333"
             ]
         }
-    }
+    },
+    "inconsistent_network_ids": []
 }
\ No newline at end of file
diff --git a/tests/fixtures/geojson_to_json/phase_funders_1.meta.expected.json b/tests/fixtures/geojson_to_json/phase_funders_1.meta.expected.json
index b2226e8..6950393 100644
--- a/tests/fixtures/geojson_to_json/phase_funders_1.meta.expected.json
+++ b/tests/fixtures/geojson_to_json/phase_funders_1.meta.expected.json
@@ -74,5 +74,6 @@
         }
     },
     "inconsistent_phases_by_network_id": {},
-    "inconsistent_organisations_by_network_id": {}
+    "inconsistent_organisations_by_network_id": {},
+    "inconsistent_network_ids": []
 }
\ No newline at end of file
diff --git a/tests/fixtures/geojson_to_json/phases_1.meta.expected.json b/tests/fixtures/geojson_to_json/phases_1.meta.expected.json
index 7166692..ee0f94a 100644
--- a/tests/fixtures/geojson_to_json/phases_1.meta.expected.json
+++ b/tests/fixtures/geojson_to_json/phases_1.meta.expected.json
@@ -107,5 +107,6 @@
         }
     },
     "inconsistent_phases_by_network_id": {},
-    "inconsistent_organisations_by_network_id": {}
+    "inconsistent_organisations_by_network_id": {},
+    "inconsistent_network_ids": []
 }
\ No newline at end of file
diff --git a/tests/fixtures/geojson_to_json/phases_inconsistent_1.expected.json b/tests/fixtures/geojson_to_json/phases_inconsistent_1.expected.json
index ae85171..e65ca4f 100644
--- a/tests/fixtures/geojson_to_json/phases_inconsistent_1.expected.json
+++ b/tests/fixtures/geojson_to_json/phases_inconsistent_1.expected.json
@@ -10,8 +10,8 @@
                     "description": "Contract for the construction of phase 1 of the NextGen network.",
                     "relatedPhases": [
                         {
-                            "id": "1",
-                            "name": "NextGen Phase 1"
+                            "id": "2",
+                            "name": "NextGen Phase 2"
                         }
                     ]
                 }
@@ -119,6 +119,11 @@
                 }
             ],
             "phases": [
+                {
+                    "id": "2",
+                    "name": "NextGen Phase 2",
+                    "description": "The second phase of the Ghana Fibre Network NextGen roll-out."
+                },
                 {
                     "id": "1",
                     "name": "NextGen Phase 1",
diff --git a/tests/fixtures/geojson_to_json/phases_inconsistent_1.meta.expected.json b/tests/fixtures/geojson_to_json/phases_inconsistent_1.meta.expected.json
index a5a7dd4..177b1f9 100644
--- a/tests/fixtures/geojson_to_json/phases_inconsistent_1.meta.expected.json
+++ b/tests/fixtures/geojson_to_json/phases_inconsistent_1.meta.expected.json
@@ -97,21 +97,25 @@
             "count": 1
         },
         "/networks/phases/id": {
-            "count": 1
+            "count": 2
         },
         "/networks/phases/name": {
-            "count": 1
+            "count": 2
         },
         "/networks/phases/description": {
-            "count": 1
+            "count": 2
         }
     },
     "inconsistent_phases_by_network_id": {
         "a096d627-72e1-4f9b-b129-951b1737bff4": {
             "phase_ids": [
-                "1"
+                "1",
+                "2"
             ]
         }
     },
-    "inconsistent_organisations_by_network_id": {}
+    "inconsistent_organisations_by_network_id": {},
+    "inconsistent_network_ids": [
+        "a096d627-72e1-4f9b-b129-951b1737bff4"
+    ]
 }
\ No newline at end of file
diff --git a/tests/fixtures/geojson_to_json/phases_inconsistent_1.nodes.geo.json b/tests/fixtures/geojson_to_json/phases_inconsistent_1.nodes.geo.json
index b25df74..66ded87 100644
--- a/tests/fixtures/geojson_to_json/phases_inconsistent_1.nodes.geo.json
+++ b/tests/fixtures/geojson_to_json/phases_inconsistent_1.nodes.geo.json
@@ -28,9 +28,9 @@
                             "description": "Contract for the construction of phase 1 of the NextGen network.",
                             "relatedPhases": [
                                 {
-                                    "id": "1",
-                                    "name": "NextGen Phase 1",
-                                    "description": "The first phase of the Ghana Fibre Network NextGen roll-out."
+                                    "id": "2",
+                                    "name": "NextGen Phase 2",
+                                    "description": "The second phase of the Ghana Fibre Network NextGen roll-out."
                                 }
                             ]
                         }
@@ -66,9 +66,9 @@
                             "description": "Contract for the construction of phase 1 of the NextGen network.",
                             "relatedPhases": [
                                 {
-                                    "id": "1",
-                                    "name": "NextGen Phase 1",
-                                    "description": "The first phase of the Ghana Fibre Network NextGen roll-out."
+                                    "id": "2",
+                                    "name": "NextGen Phase II",
+                                    "description": "The 2nd phase of the Ghana Fibre Network NextGen roll-out."
                                 }
                             ]
                         }
diff --git a/tests/test_geojson_to_json.py b/tests/test_geojson_to_json.py
index e392162..1263e8d 100644
--- a/tests/test_geojson_to_json.py
+++ b/tests/test_geojson_to_json.py
@@ -17,6 +17,7 @@
     # Check for errors in meta
     ("phases_inconsistent_1"),
     ("organisations_inconsistent_1"),
+    ("network_inconsistent_1"),
 ]