diff --git a/app/broadcast_areas/utils.py b/app/broadcast_areas/utils.py
index 26da631cb..fdcc1f83a 100644
--- a/app/broadcast_areas/utils.py
+++ b/app/broadcast_areas/utils.py
@@ -1,9 +1,12 @@
+from collections import defaultdict
+
 from app.broadcast_areas.models import CustomBroadcastArea
 
 
 def aggregate_areas(areas):
     areas = _convert_custom_areas_to_wards(areas)
     areas = _aggregate_wards_by_local_authority(areas)
+    areas = _aggregate_lower_tier_authorities(areas)
     return areas
 
 
@@ -24,3 +27,39 @@ def _aggregate_wards_by_local_authority(areas):
         area.parent if area.id.startswith('wd20-')
         else area for area in areas
     }
+
+
+def _aggregate_lower_tier_authorities(areas):
+    results = set()
+    clusters = _cluster_lower_tier_authorities(areas)
+
+    for cluster in clusters:
+        # always keep lone area as itself
+        if len(cluster) == 1:
+            results |= set(cluster)
+        # aggregate multi-area cluster
+        elif len(cluster) > 3:
+            results |= {cluster[0].parent}
+        # aggregate many small clusters
+        elif len(clusters) > 1:
+            area = cluster[0]
+            results |= {area.parent or area}
+        # keep one small cluster in full
+        else:
+            results |= set(cluster)
+
+    return results
+
+
+def _cluster_lower_tier_authorities(areas):
+    result = defaultdict(lambda: [])
+
+    for area in areas:
+        # group lower tier authorities by "county"
+        if area.id.startswith('lad20-') and area.parent:
+            result[area.parent] += [area]
+        # leave countries, unitary authorities as-is
+        else:
+            result[area] = [area]
+
+    return result.values()
diff --git a/tests/app/broadcast_areas/custom_polygons.py b/tests/app/broadcast_areas/custom_polygons.py
index 03a0dcc47..e79360649 100644
--- a/tests/app/broadcast_areas/custom_polygons.py
+++ b/tests/app/broadcast_areas/custom_polygons.py
@@ -37,3 +37,19 @@ CHELTENHAM = [
     [51.9328, -2.0221],
     [51.9324, -2.1265],
 ]
+
+CHELTENHAM_AND_GLOUCESTER = [
+    [51.8820, -2.2920],
+    [51.8234, -2.2570],
+    [51.8883, -2.0262],
+    [51.9425, -2.0771],
+    [51.8820, -2.2920],
+]
+
+SEVERN_ESTUARY = [
+    [51.5719, -2.9388],
+    [51.4180, -2.7259],
+    [51.8493, -2.1958],
+    [51.8883, -2.3016],
+    [51.5719, -2.9388],
+]
diff --git a/tests/app/broadcast_areas/test_utils.py b/tests/app/broadcast_areas/test_utils.py
index 74e940fcc..c95b75eff 100644
--- a/tests/app/broadcast_areas/test_utils.py
+++ b/tests/app/broadcast_areas/test_utils.py
@@ -7,12 +7,24 @@ from tests.app.broadcast_areas.custom_polygons import (
     BRISTOL,
     BURFORD,
     CHELTENHAM,
+    CHELTENHAM_AND_GLOUCESTER,
     SANTA_A,
+    SEVERN_ESTUARY,
     SKYE,
 )
 
 
 @pytest.mark.parametrize(('area_ids', 'expected_area_names'), [
+    (
+        [
+            'wd20-E05009336',  # Whitechapel, Tower Hamlets (electoral ward)
+            'wd20-E05009372',  # Hackney Central, Hackney (electoral ward)
+            'wd20-E05009374',  # Hackney Wick, Hackney (electoral ward)
+        ], [
+            'Hackney',  # in Greater London* (DB doesn't know this)
+            'Tower Hamlets',  # in Greater London*
+        ],
+    ),
     (
         [
             'wd20-E05004294',  # Hester’s Way, Cheltenham (electoral ward)
@@ -31,6 +43,16 @@ from tests.app.broadcast_areas.custom_polygons import (
             'Hackney',  # in Greater London* (DB doesn't know this)
         ],
     ),
+    (
+        [
+            'wd20-E05004294',  # Hester’s Way, Cheltenham (electoral ward)
+            'wd20-E05010981',  # Painswick & Upton, Stroud (electoral ward)
+            'wd20-E05009372',  # Hackney Central, Hackney (electoral ward)
+        ], [
+            'Gloucestershire',  # upper tier authority
+            'Hackney',  # in Greater London* (DB doesn't know this)
+        ],
+    ),
     (
         [
             'lad20-E07000037',  # High Peak (lower tier authority)
@@ -49,6 +71,17 @@ from tests.app.broadcast_areas.custom_polygons import (
             'High Peak',  # in Derbyshire
         ]
     ),
+    (
+        [
+            'lad20-E07000037',  # High Peak (lower tier authority)
+            'lad20-E07000035',  # Derbyshire Dales (lower tier authority)
+            'ctyua19-E10000028',  # Staffordshire (upper tier authority)
+        ],
+        [
+            'Derbyshire',  # upper tier authority
+            'Staffordshire',
+        ]
+    ),
     (
         [
             'ctry19-E92000001',  # England
@@ -84,6 +117,19 @@ def test_aggregate_areas(
             'Bristol, City of',
         ]
     ),
+    (
+        [SEVERN_ESTUARY], [
+            # Area covers various lower-tier authorities
+            # with more than three in Gloucestershire so
+            # we aggregate them into that
+            'Bristol, City of',
+            'Gloucestershire',
+            'Monmouthshire',
+            'Newport',
+            'North Somerset',
+            'South Gloucestershire',
+        ]
+    ),
     (
         [CHELTENHAM], [
             # Area covers three lower-tier authorities
@@ -93,14 +139,30 @@ def test_aggregate_areas(
             'Tewkesbury',
         ]
     ),
+    (
+        [CHELTENHAM_AND_GLOUCESTER], [
+            # Area covers more than 3 lower-tier authorities
+            # in Gloucestershire so we aggregate them
+            'Gloucestershire',
+        ]
+    ),
     (
         [BURFORD], [
-            # Area covers two lower-tier authorities
-            # in Gloucestershire (upper tier authority)
+            # Area covers one lower-tier authority in
+            # Gloucestershire and one in Oxfordshire (both
+            # upper tier authorities)
             'Cotswold',
             'West Oxfordshire',
         ],
     ),
+    (
+        [CHELTENHAM_AND_GLOUCESTER, BURFORD], [
+            # Area covers many lower-tier authorities
+            # in Gloucestershire but only one in Oxfordshire
+            'Gloucestershire',
+            'West Oxfordshire',
+        ],
+    ),
     (
         [SANTA_A], [
             # Does not overlap with the UK