diff --git a/app/broadcast_areas/models.py b/app/broadcast_areas/models.py
index 6084cd7c9..8d364e3c5 100644
--- a/app/broadcast_areas/models.py
+++ b/app/broadcast_areas/models.py
@@ -86,6 +86,14 @@ class BroadcastArea(BaseBroadcastArea, SortableMixin):
     def __init__(self, row):
         self.id, self.name, self._count_of_phones, self.library_id = row
 
+    @cached_property
+    def is_lower_tier_local_authority(self):
+        return self.id.startswith('lad20-') and self.parent
+
+    @cached_property
+    def is_electoral_ward(self):
+        return self.id.startswith('wd20-')
+
     @classmethod
     def from_row_with_simple_polygons(cls, row):
         instance = cls(row[:4])
@@ -127,6 +135,10 @@ class BroadcastArea(BaseBroadcastArea, SortableMixin):
     def ancestors(self):
         return list(self._ancestors_iterator)
 
+    @cached_property
+    def parent(self):
+        return next(iter(self.ancestors), None)
+
     @property
     def _ancestors_iterator(self):
         id = self.id
@@ -162,6 +174,13 @@ class CustomBroadcastArea(BaseBroadcastArea):
 
     simple_polygons = polygons
 
+    @cached_property
+    def overlapping_electoral_wards(self):
+        return [
+            area for area in self.nearby_electoral_wards
+            if area.simple_polygons.intersects(self.polygons)
+        ]
+
     @cached_property
     def nearby_electoral_wards(self):
         if not self.polygons:
diff --git a/app/broadcast_areas/utils.py b/app/broadcast_areas/utils.py
new file mode 100644
index 000000000..48766073d
--- /dev/null
+++ b/app/broadcast_areas/utils.py
@@ -0,0 +1,65 @@
+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 sorted(areas)
+
+
+def _convert_custom_areas_to_wards(areas):
+    results = set()
+
+    for area in areas:
+        if type(area) == CustomBroadcastArea:
+            results |= set(area.overlapping_electoral_wards)
+        else:
+            results |= {area}
+
+    return results
+
+
+def _aggregate_wards_by_local_authority(areas):
+    return {
+        area.parent if area.is_electoral_ward
+        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 show a single area cluster as itself (aggregation isn't helpful)
+        if len(cluster) == 1:
+            results |= set(cluster)
+        # aggregate a single cluster with lots of areas (too complex to show in full)
+        elif len(cluster) > 3:
+            results |= {cluster[0].parent}
+        # if cluster is 2 or 3 areas, and there are more than 1 cluster, aggregate the cluster
+        elif len(clusters) > 1:
+            area = cluster[0]
+            results |= {area.parent or area}
+        # else keep single 2-3 areas cluster in full (easy enough to understand)
+        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.is_lower_tier_local_authority:
+            result[area.parent] += [area]
+        # leave countries, unitary authorities as-is
+        else:
+            result[area] = [area]
+
+    return result.values()
diff --git a/app/models/broadcast_message.py b/app/models/broadcast_message.py
index 8b9878a8c..5e1a5deb4 100644
--- a/app/models/broadcast_message.py
+++ b/app/models/broadcast_message.py
@@ -11,6 +11,7 @@ from app.broadcast_areas.models import (
     CustomBroadcastAreas,
     broadcast_area_libraries,
 )
+from app.broadcast_areas.utils import aggregate_areas
 from app.formatters import round_to_significant_figures
 from app.models import JSONModel, ModelList
 from app.models.user import User
@@ -244,6 +245,7 @@ class BroadcastMessage(JSONModel):
         areas = {
             'ids': self.area_ids,
             'names': [area.name for area in self.areas],
+            'aggregate_names': [area.name for area in aggregate_areas(self.areas)],
             'simple_polygons': self.simple_polygons.as_coordinate_pairs_lat_long
         }
 
diff --git a/tests/__init__.py b/tests/__init__.py
index 27785c65c..95bd17233 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -667,11 +667,11 @@ def find_element_by_tag_and_partial_text(page, tag, string):
 
 def broadcast_message_json(
     *,
-    id_,
-    service_id,
-    template_id,
-    status,
-    created_by_id,
+    id_=None,
+    service_id=None,
+    template_id=None,
+    status='draft',
+    created_by_id=None,
     starts_at=None,
     finishes_at=None,
     cancelled_at=None,
diff --git a/tests/app/broadcast_areas/custom_polygons.py b/tests/app/broadcast_areas/custom_polygons.py
index 6faea8675..e79360649 100644
--- a/tests/app/broadcast_areas/custom_polygons.py
+++ b/tests/app/broadcast_areas/custom_polygons.py
@@ -13,3 +13,43 @@ SKYE = [
     [57.7334, -6.8280],
     [57.1004, -6.8280],
 ]
+
+SANTA_A = [
+    [25.8890, 66.5500],
+    [25.8890, 66.551],
+    [25.8910, 66.551],
+    [25.8910, 66.5500],
+    [25.889, 66.55000],
+]
+
+BURFORD = [
+    [51.8925, -1.7495],
+    [51.7372, -1.7825],
+    [51.7159, -1.5257],
+    [51.8866, -1.5037],
+    [51.8925, -1.7495],
+]
+
+CHELTENHAM = [
+    [51.9324, -2.1265],
+    [51.8633, -2.1306],
+    [51.8637, -2.0242],
+    [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_models.py b/tests/app/broadcast_areas/test_models.py
new file mode 100644
index 000000000..23b9933d2
--- /dev/null
+++ b/tests/app/broadcast_areas/test_models.py
@@ -0,0 +1,20 @@
+import pytest
+
+from app.broadcast_areas.models import CustomBroadcastArea
+from tests.app.broadcast_areas.custom_polygons import BRISTOL, SANTA_A, SKYE
+
+
+@pytest.mark.parametrize(('simple_polygon', 'expected_wards_length'), [
+    (SKYE, 2),
+    (BRISTOL, 12),
+    (SANTA_A, 0)  # does not overlap with UK
+])
+def test_custom_broadcast_area_overlapping_electoral_wards(
+    simple_polygon,
+    expected_wards_length,
+):
+    custom_area = CustomBroadcastArea(
+        name='foo', polygons=[simple_polygon]
+    )
+
+    assert len(custom_area.overlapping_electoral_wards) == expected_wards_length
diff --git a/tests/app/broadcast_areas/test_utils.py b/tests/app/broadcast_areas/test_utils.py
new file mode 100644
index 000000000..8ed121995
--- /dev/null
+++ b/tests/app/broadcast_areas/test_utils.py
@@ -0,0 +1,185 @@
+import pytest
+
+from app.broadcast_areas.utils import aggregate_areas
+from app.models.broadcast_message import BroadcastMessage
+from tests import broadcast_message_json
+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)
+            'wd20-E05010981',  # Painswick & Upton, Stroud (electoral ward)
+        ], [
+            'Cheltenham',  # in Gloucestershire (upper tier authority)
+            'Stroud',  # in Gloucestershire
+        ],
+    ),
+    (
+        [
+            'wd20-E05004294',  # Hester’s Way, Cheltenham (electoral ward)
+            'wd20-E05009372',  # Hackney Central (electoral ward)
+        ], [
+            'Cheltenham',  # in Gloucestershire (upper tier authority)
+            '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)
+        ],
+        [
+            'High Peak',  # in Derbyshire (upper tier authority)
+        ]
+    ),
+    (
+        [
+            'lad20-E07000037',  # High Peak (lower tier authority)
+            'lad20-E07000035',  # Derbyshire Dales (lower tier authority)
+        ],
+        [
+            'Derbyshire Dales',  # in Derbyshire (upper tier authority)
+            '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
+        ],
+        [
+            'England',
+        ]
+    )
+])
+def test_aggregate_areas(
+    area_ids,
+    expected_area_names,
+):
+    broadcast_message = BroadcastMessage(
+        broadcast_message_json(area_ids=area_ids)
+    )
+
+    assert [
+        area.name for area in aggregate_areas(broadcast_message.areas)
+    ] == expected_area_names
+
+
+@pytest.mark.parametrize(('simple_polygons', 'expected_area_names'), [
+    (
+        [SKYE], [
+            # Area covers a single unitary authority
+            'Highland',
+        ]
+    ),
+    (
+        [BRISTOL], [
+            # Area covers a single unitary authority
+            '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
+            # in Gloucestershire (upper tier authority)
+            'Cheltenham',
+            'Cotswold',
+            'Tewkesbury',
+        ]
+    ),
+    (
+        [CHELTENHAM_AND_GLOUCESTER], [
+            # Area covers more than 3 lower-tier authorities
+            # in Gloucestershire so we aggregate them
+            'Gloucestershire',
+        ]
+    ),
+    (
+        [BURFORD], [
+            # 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
+        ],
+    ),
+])
+def test_aggregate_areas_for_custom_polygons(
+    simple_polygons,
+    expected_area_names,
+):
+    broadcast_message = BroadcastMessage(
+        broadcast_message_json(
+            area_ids=['derived from polygons'],
+            simple_polygons=simple_polygons
+        )
+    )
+
+    assert [
+        area.name for area in aggregate_areas(broadcast_message.areas)
+    ] == expected_area_names
diff --git a/tests/app/main/views/test_broadcast.py b/tests/app/main/views/test_broadcast.py
index 414b1502c..e50b0a858 100644
--- a/tests/app/main/views/test_broadcast.py
+++ b/tests/app/main/views/test_broadcast.py
@@ -1398,6 +1398,7 @@ def test_add_broadcast_area(
             'areas': {
                 'ids': ['ctry19-E92000001', 'ctry19-S92000003', 'ctry19-W92000004'],
                 'names': ['England', 'Scotland', 'Wales'],
+                'aggregate_names': ['England', 'Scotland', 'Wales'],
                 'simple_polygons': coordinates
             }
         },
@@ -1411,7 +1412,9 @@ def test_add_broadcast_area(
         },
         {
             # wd20-S13002845 is ignored because the user chose ‘Select all…’
-            'ids': ['lad20-S12000033'], 'names': ['Aberdeen City']
+            'ids': ['lad20-S12000033'],
+            'names': ['Aberdeen City'],
+            'aggregate_names': ['Aberdeen City']
         }
     ),
     (
@@ -1421,6 +1424,7 @@ def test_add_broadcast_area(
         {
             'ids': ['wd20-S13002845', 'wd20-S13002836'],
             'names': ['Bridge of Don', 'Airyhall/Broomhill/Garthdee'],
+            'aggregate_names': ['Aberdeen City'],
         }
     ),
 ))
@@ -1454,6 +1458,7 @@ def test_add_broadcast_sub_area_district_view(
     # These two areas are on the broadcast already
     expected_data['ids'] = ['ctry19-E92000001', 'ctry19-S92000003'] + expected_data['ids']
     expected_data['names'] = ['England', 'Scotland'] + expected_data['names']
+    expected_data['aggregate_names'] = sorted(['England', 'Scotland'] + expected_data['aggregate_names'])
 
     mock_update_broadcast_message.assert_called_once_with(
         service_id=SERVICE_ONE_ID,
@@ -1504,7 +1509,8 @@ def test_add_broadcast_sub_area_county_view(
                 ] + [
                     'ctyua19-E10000016'
                 ],
-                'names': ['England', 'Scotland', 'Kent']
+                'names': ['England', 'Scotland', 'Kent'],
+                'aggregate_names': ['England', 'Kent', 'Scotland']
             }
         },
     )
@@ -1545,6 +1551,7 @@ def test_remove_broadcast_area_page(
             'areas': {
                 'simple_polygons': coordinates,
                 'names': ['Scotland'],
+                'aggregate_names': ['Scotland'],
                 'ids': ['ctry19-S92000003']
             },
         },