diff --git a/home/forms/search.py b/home/forms/search.py
index 70449642..90a8e3b8 100644
--- a/home/forms/search.py
+++ b/home/forms/search.py
@@ -1,28 +1,22 @@
 from copy import deepcopy
 from urllib.parse import urlencode
 
-from data_platform_catalogue.search_types import ResultType
+from data_platform_catalogue.search_types import DomainOption, ResultType
 from django import forms
 
-from ..models.domain_model import Domain, DomainModel
-from ..service.search_facet_fetcher import SearchFacetFetcher
+from ..models.domain_model import Domain
+from ..service.domain_fetcher import DomainFetcher
 from ..service.search_tag_fetcher import SearchTagFetcher
 
 
 def get_domain_choices() -> list[Domain]:
-    """Make API call to obtain domain choices"""
+    """Make Domains API call to obtain domain choices"""
     choices = [
         Domain("", "All domains"),
     ]
-    facets = SearchFacetFetcher().fetch()
-    choices.extend(DomainModel(facets).top_level_domains)
-    return choices
-
-
-def get_subdomain_choices() -> list[Domain]:
-    choices = [Domain("", "All subdomains")]
-    facets = SearchFacetFetcher().fetch()
-    choices.extend(DomainModel(facets).all_subdomains())
+    list_domain_options: list[DomainOption] = DomainFetcher().fetch()
+    domains: list[Domain] = [Domain(d.urn, d.name) for d in list_domain_options]
+    choices.extend(domains)
     return choices
 
 
@@ -53,27 +47,6 @@ def get_tags():
     return tags
 
 
-class SelectWithOptionAttribute(forms.Select):
-    def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs)
-        self.domain_model = None
-
-    def create_option(
-        self, name, urn, label, selected, index, subindex=None, attrs=None
-    ):
-        option = super().create_option(
-            name, urn, label, selected, index, subindex, attrs
-        )
-
-        facets = SearchFacetFetcher().fetch()
-        self.domain_model = self.domain_model or DomainModel(facets)
-
-        if urn:
-            option["attrs"]["data-parent"] = self.domain_model.get_parent_urn(urn)
-
-        return option
-
-
 class SearchForm(forms.Form):
     """Django form to represent search page inputs"""
 
@@ -97,13 +70,6 @@ class SearchForm(forms.Form):
             }
         ),
     )
-    subdomain = forms.ChoiceField(
-        choices=get_subdomain_choices,
-        required=False,
-        widget=SelectWithOptionAttribute(
-            attrs={"form": "searchform", "class": "govuk-select"}
-        ),
-    )
     where_to_access = forms.MultipleChoiceField(
         choices=get_where_to_access_choices,
         required=False,
@@ -171,6 +137,4 @@ def encode_without_filter(self, filter_name: str, filter_value: str):
             value.remove(filter_value)
         elif isinstance(value, str) and filter_value == value:
             query_params.pop(filter_name)
-            if filter_name == "domain":
-                query_params.pop("subdomain")
         return f"?{urlencode(query_params, doseq=True)}"
diff --git a/home/models/domain_model.py b/home/models/domain_model.py
index c0b96dbd..b06cdb3f 100644
--- a/home/models/domain_model.py
+++ b/home/models/domain_model.py
@@ -1,7 +1,7 @@
 import logging
 from typing import NamedTuple
 
-from data_platform_catalogue.search_types import SearchFacets
+from data_platform_catalogue.search_types import DomainOption
 
 logger = logging.getLogger(__name__)
 
@@ -12,40 +12,14 @@ class Domain(NamedTuple):
 
 
 class DomainModel:
-    """
-    Store information about domains and subdomains
-    """
-
-    def __init__(self, search_facets: SearchFacets):
+    def __init__(self, domains: list[DomainOption]):
         self.labels = {}
 
-        self.top_level_domains = [
-            Domain(option.value, option.label)
-            for option in search_facets.options("domains")
-        ]
-        self.top_level_domains.sort(key=lambda d: d.label)
-
+        self.top_level_domains = [Domain(domain.urn, domain.name) for domain in domains]
         logger.info(f"{self.top_level_domains=}")
 
-        self.subdomains = {}
-
         for urn, label in self.top_level_domains:
             self.labels[urn] = label
 
-    def all_subdomains(self) -> list[Domain]:  # -> list[Any]
-        """
-        A flat list of all subdomains
-        """
-        subdomains = []
-        for domain_choices in self.subdomains.values():
-            subdomains.extend(domain_choices)
-        return subdomains
-
-    def get_parent_urn(self, child_subdomain_urn) -> str | None:
-        for domain, subdomains in self.subdomains.items():
-            for subdomain in subdomains:
-                if child_subdomain_urn == subdomain.urn:
-                    return domain
-
     def get_label(self, urn):
         return self.labels.get(urn, urn)
diff --git a/home/service/list_domain_fetcher.py b/home/service/domain_fetcher.py
similarity index 80%
rename from home/service/list_domain_fetcher.py
rename to home/service/domain_fetcher.py
index 10d4a6e9..f15e3e3c 100644
--- a/home/service/list_domain_fetcher.py
+++ b/home/service/domain_fetcher.py
@@ -1,12 +1,12 @@
-from data_platform_catalogue.search_types import ListDomainOption
+from data_platform_catalogue.search_types import DomainOption
 from django.core.cache import cache
 
 from .base import GenericService
 
 
-class ListDomainFetcher(GenericService):
+class DomainFetcher(GenericService):
     """
-    ListDomainFetcher implementation to fetch domains with the total number of
+    DomainFetcher implementation to fetch domains with the total number of
     associated entities from the backend.
     """
 
@@ -16,7 +16,7 @@ def __init__(self, filter_zero_entities: bool = True):
         self.cache_timeout_seconds = 300
         self.filter_zero_entities = filter_zero_entities
 
-    def fetch(self) -> list[ListDomainOption]:
+    def fetch(self) -> list[DomainOption]:
         """
         Fetch a static list of options that is independent of the search query
         and any applied filters. Values are cached for 5 seconds to avoid
diff --git a/home/service/search.py b/home/service/search.py
index ef197517..fc69df93 100644
--- a/home/service/search.py
+++ b/home/service/search.py
@@ -3,6 +3,7 @@
 from typing import Any
 
 from data_platform_catalogue.search_types import (
+    DomainOption,
     MultiSelectFilter,
     ResultType,
     SearchResponse,
@@ -16,32 +17,13 @@
 from home.models.domain_model import DomainModel
 
 from .base import GenericService
-from .search_facet_fetcher import SearchFacetFetcher
-
-
-def domains_with_their_subdomains(
-    domain: str, subdomain: str, domain_model: DomainModel
-) -> list[str]:
-    """
-    Users can search by domain, and optionally by subdomain.
-    When subdomain is passed, then we can filter on that directly.
-
-    However, when we filter by domain alone, assets tagged to subdomains
-    are not automatically included, so we need to include all possible
-    subdomains in the filter.
-    """
-    if subdomain:
-        return [subdomain]
-
-    subdomains = domain_model.subdomains.get(domain, [])
-    subdomains = [subdomain[0] for subdomain in subdomains]
-    return [domain, *subdomains] if not domain == "" else []
+from .domain_fetcher import DomainFetcher
 
 
 class SearchService(GenericService):
     def __init__(self, form: SearchForm, page: str, items_per_page: int = 20):
-        facets = SearchFacetFetcher().fetch()
-        self.domain_model = DomainModel(facets)
+        domains: list[DomainOption] = DomainFetcher().fetch()
+        self.domain_model = DomainModel(domains)
         self.stemmer = PorterStemmer()
         self.form = form
         if self.form.is_bound:
@@ -79,18 +61,14 @@ def _get_search_results(self, page: str, items_per_page: int) -> SearchResponse:
         query = form_data.get("query", "").replace("_", " ")
         sort = form_data.get("sort", "relevance")
         domain = form_data.get("domain", "")
-        subdomain = form_data.get("subdomain", "")
         tags = form_data.get("tags", "")
-        domains_and_subdomains = domains_with_their_subdomains(
-            domain, subdomain, self.domain_model
-        )
         where_to_access = self._build_custom_property_filter(
             "dc_where_to_access_dataset=", form_data.get("where_to_access", [])
         )
         entity_types = self._build_entity_types(form_data.get("entity_types", []))
         filter_value = []
-        if domains_and_subdomains:
-            filter_value.append(MultiSelectFilter("domains", domains_and_subdomains))
+        if domain:
+            filter_value.append(MultiSelectFilter("domains", [domain]))
         if where_to_access:
             filter_value.append(MultiSelectFilter("customProperties", where_to_access))
         if tags:
@@ -167,9 +145,8 @@ def _generate_domain_clear_href(
         self,
     ) -> dict[str, str]:
         domain = self.form.cleaned_data.get("domain", "")
-        subdomain = self.form.cleaned_data.get("subdomain", "")
 
-        label = self.domain_model.get_label(subdomain or domain)
+        label = self.domain_model.get_label(domain)
 
         return {
             label: (
diff --git a/home/views.py b/home/views.py
index 864bf9e6..903f7d2c 100644
--- a/home/views.py
+++ b/home/views.py
@@ -1,5 +1,5 @@
 from data_platform_catalogue.client.exceptions import EntityDoesNotExist
-from data_platform_catalogue.search_types import ListDomainOption
+from data_platform_catalogue.search_types import DomainOption
 from django.http import Http404, HttpResponseBadRequest
 from django.shortcuts import render
 
@@ -9,8 +9,8 @@
     DatabaseDetailsService,
     DatasetDetailsService,
 )
+from home.service.domain_fetcher import DomainFetcher
 from home.service.glossary import GlossaryService
-from home.service.list_domain_fetcher import ListDomainFetcher
 from home.service.metadata_specification import MetadataSpecificationService
 from home.service.search import SearchService
 
@@ -19,7 +19,7 @@ def home_view(request):
     """
     Displys only domains that have entities tagged for display in the catalog.
     """
-    domains: list[ListDomainOption] = ListDomainFetcher().fetch()
+    domains: list[DomainOption] = DomainFetcher().fetch()
     context = {"domains": domains, "h1_value": "Home"}
     return render(request, "home.html", context)
 
diff --git a/lib/datahub-client/data_platform_catalogue/client/datahub_client.py b/lib/datahub-client/data_platform_catalogue/client/datahub_client.py
index 7b762ded..42233d8a 100644
--- a/lib/datahub-client/data_platform_catalogue/client/datahub_client.py
+++ b/lib/datahub-client/data_platform_catalogue/client/datahub_client.py
@@ -3,30 +3,6 @@
 from importlib.resources import files
 from typing import Sequence
 
-from datahub.configuration.common import ConfigurationError
-from datahub.emitter import mce_builder
-from datahub.emitter.mcp import MetadataChangeProposalWrapper
-from datahub.ingestion.graph.client import DatahubClientConfig, DataHubGraph
-from datahub.ingestion.source.common.subtypes import (
-    DatasetContainerSubTypes,
-    DatasetSubTypes,
-)
-from datahub.metadata import schema_classes
-from datahub.metadata.com.linkedin.pegasus2avro.common import DataPlatformInstance
-from datahub.metadata.schema_classes import (
-    ChangeTypeClass,
-    ContainerClass,
-    ContainerPropertiesClass,
-    DatasetPropertiesClass,
-    DomainPropertiesClass,
-    DomainsClass,
-    OtherSchemaClass,
-    SchemaFieldClass,
-    SchemaFieldDataTypeClass,
-    SchemaMetadataClass,
-    SubTypesClass,
-)
-
 from data_platform_catalogue.client.exceptions import (
     AspectDoesNotExist,
     ConnectivityError,
@@ -57,13 +33,36 @@
     Table,
 )
 from data_platform_catalogue.search_types import (
-    ListDomainOption,
+    DomainOption,
     MultiSelectFilter,
     ResultType,
     SearchFacets,
     SearchResponse,
     SortOption,
 )
+from datahub.configuration.common import ConfigurationError
+from datahub.emitter import mce_builder
+from datahub.emitter.mcp import MetadataChangeProposalWrapper
+from datahub.ingestion.graph.client import DatahubClientConfig, DataHubGraph
+from datahub.ingestion.source.common.subtypes import (
+    DatasetContainerSubTypes,
+    DatasetSubTypes,
+)
+from datahub.metadata import schema_classes
+from datahub.metadata.com.linkedin.pegasus2avro.common import DataPlatformInstance
+from datahub.metadata.schema_classes import (
+    ChangeTypeClass,
+    ContainerClass,
+    ContainerPropertiesClass,
+    DatasetPropertiesClass,
+    DomainPropertiesClass,
+    DomainsClass,
+    OtherSchemaClass,
+    SchemaFieldClass,
+    SchemaFieldDataTypeClass,
+    SchemaMetadataClass,
+    SubTypesClass,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -230,9 +229,9 @@ def list_domains(
             MultiSelectFilter("tags", ["urn:li:tag:dc_display_in_catalogue"])
         ],
         count: int = 1000,
-    ) -> list[ListDomainOption]:
+    ) -> list[DomainOption]:
         """
-        Returns a list of ListDomainOption objects
+        Returns a list of DomainOption objects
         """
         return self.search_client.list_domains(
             query=query, filters=filters, count=count
diff --git a/lib/datahub-client/data_platform_catalogue/client/search.py b/lib/datahub-client/data_platform_catalogue/client/search.py
index 7117e1e3..e27967dc 100644
--- a/lib/datahub-client/data_platform_catalogue/client/search.py
+++ b/lib/datahub-client/data_platform_catalogue/client/search.py
@@ -3,9 +3,6 @@
 from importlib.resources import files
 from typing import Any, Sequence
 
-from datahub.configuration.common import GraphError  # pylint: disable=E0611
-from datahub.ingestion.graph.client import DataHubGraph  # pylint: disable=E0611
-
 from data_platform_catalogue.client.exceptions import CatalogueError
 from data_platform_catalogue.client.graphql_helpers import (
     parse_created_and_modified,
@@ -19,8 +16,8 @@
 )
 from data_platform_catalogue.entities import EntityRef
 from data_platform_catalogue.search_types import (
+    DomainOption,
     FacetOption,
-    ListDomainOption,
     MultiSelectFilter,
     ResultType,
     SearchFacets,
@@ -28,6 +25,8 @@
     SearchResult,
     SortOption,
 )
+from datahub.configuration.common import GraphError  # pylint: disable=E0611
+from datahub.ingestion.graph.client import DataHubGraph  # pylint: disable=E0611
 
 logger = logging.getLogger(__name__)
 
@@ -193,7 +192,7 @@ def list_domains(
             MultiSelectFilter("tags", ["urn:li:tag:dc_display_in_catalogue"])
         ],
         count: int = 1000,
-    ) -> list[ListDomainOption]:
+    ) -> list[DomainOption]:
         """
         Returns domains that can be used to filter the search results.
         """
@@ -255,8 +254,8 @@ def _map_filters(self, filters: Sequence[MultiSelectFilter]):
 
     def _parse_list_domains(
         self, list_domains_result: list[dict[str, Any]]
-    ) -> list[ListDomainOption]:
-        list_domain_options: list[ListDomainOption] = []
+    ) -> list[DomainOption]:
+        list_domain_options: list[DomainOption] = []
 
         for domain in list_domains_result:
             urn = domain.get("urn", "")
@@ -265,7 +264,7 @@ def _parse_list_domains(
             entities = domain.get("entities", {})
             total = entities.get("total", 0)
 
-            list_domain_options.append(ListDomainOption(urn, name, total))
+            list_domain_options.append(DomainOption(urn, name, total))
         return list_domain_options
 
     def _parse_result(
diff --git a/lib/datahub-client/data_platform_catalogue/search_types.py b/lib/datahub-client/data_platform_catalogue/search_types.py
index b09a1628..16a6b704 100644
--- a/lib/datahub-client/data_platform_catalogue/search_types.py
+++ b/lib/datahub-client/data_platform_catalogue/search_types.py
@@ -55,7 +55,7 @@ class FacetOption:
 
 
 @dataclass
-class ListDomainOption:
+class DomainOption:
     """
     A representation of a domain and the number of associated entities
     represented by total.
diff --git a/lib/datahub-client/tests/test_integration_with_datahub_server.py b/lib/datahub-client/tests/test_integration_with_datahub_server.py
index 65342866..60b94362 100644
--- a/lib/datahub-client/tests/test_integration_with_datahub_server.py
+++ b/lib/datahub-client/tests/test_integration_with_datahub_server.py
@@ -12,7 +12,6 @@
 from datetime import datetime, timezone
 
 import pytest
-
 from data_platform_catalogue.client.datahub_client import DataHubCatalogueClient
 from data_platform_catalogue.entities import (
     AccessInformation,
@@ -32,7 +31,7 @@
     UsageRestrictions,
 )
 from data_platform_catalogue.search_types import (
-    ListDomainOption,
+    DomainOption,
     MultiSelectFilter,
     ResultType,
 )
@@ -48,7 +47,7 @@ def test_list_domains():
     response = client.list_domains()
     assert len(response) > 0
     domain = response[0]
-    assert isinstance(domain, ListDomainOption)
+    assert isinstance(domain, DomainOption)
     assert "urn:li:domain" in domain.urn
 
 
diff --git a/tests/conftest.py b/tests/conftest.py
index 77490b3e..b70e0489 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -26,8 +26,8 @@
     UsageRestrictions,
 )
 from data_platform_catalogue.search_types import (
+    DomainOption,
     FacetOption,
-    ListDomainOption,
     ResultType,
     SearchFacets,
     SearchResponse,
@@ -40,7 +40,7 @@
 from home.forms.search import SearchForm
 from home.models.domain_model import DomainModel
 from home.service.details import DatabaseDetailsService
-from home.service.list_domain_fetcher import ListDomainFetcher
+from home.service.domain_fetcher import DomainFetcher
 from home.service.search import SearchService
 from home.service.search_facet_fetcher import SearchFacetFetcher
 from home.service.search_tag_fetcher import SearchTagFetcher
@@ -294,22 +294,22 @@ def mock_catalogue(request, example_database):
     mock_list_domains_response(
         mock_catalogue,
         domains=[
-            ListDomainOption(
+            DomainOption(
                 urn="urn:li:domain:prisons",
                 name="Prisons",
                 total=fake.random_int(min=1, max=100),
             ),
-            ListDomainOption(
+            DomainOption(
                 urn="urn:li:domain:courts",
                 name="Courts",
                 total=fake.random_int(min=1, max=100),
             ),
-            ListDomainOption(
+            DomainOption(
                 urn="urn:li:domain:finance",
                 name="Finance",
                 total=fake.random_int(min=1, max=100),
             ),
-            ListDomainOption(
+            DomainOption(
                 urn="urn:li:domain:hq",
                 name="HQ",
                 total=0,
@@ -443,7 +443,7 @@ def search_facets():
 
 @pytest.fixture
 def list_domains(filter_zero_entities):
-    return ListDomainFetcher(filter_zero_entities).fetch()
+    return DomainFetcher(filter_zero_entities).fetch()
 
 
 @pytest.fixture
@@ -452,8 +452,11 @@ def search_tags():
 
 
 @pytest.fixture
-def valid_domain(search_facets):
-    return DomainModel(search_facets).top_level_domains[0]
+def valid_domain():
+    domains = DomainFetcher().fetch()
+    return DomainModel(
+        domains,
+    ).top_level_domains[0]
 
 
 @pytest.fixture
diff --git a/tests/home/service/test_search.py b/tests/home/service/test_search.py
index 83545492..96cfebc3 100644
--- a/tests/home/service/test_search.py
+++ b/tests/home/service/test_search.py
@@ -6,7 +6,7 @@
 import pytest
 
 from home.forms.search import SearchForm
-from home.service.search import SearchService, domains_with_their_subdomains
+from home.service.search import SearchService
 
 dev_env = True if os.environ.get("ENV") == "dev" else False
 run_for_dev = pytest.mark.skipif(
@@ -48,7 +48,6 @@ def test_get_context_remove_filter_hrefs(self, search_context, valid_domain):
             "analytical_platform": (
                 "?query=test&"
                 f"domain={quote(valid_domain.urn)}&"
-                "subdomain=&"
                 "entity_types=TABLE&"
                 "sort=ascending&"
                 "clear_filter=False&"
@@ -61,7 +60,6 @@ def test_get_context_remove_filter_hrefs(self, search_context, valid_domain):
             "Table": (
                 "?query=test&"
                 f"domain={quote(valid_domain.urn)}&"
-                "subdomain=&"
                 "where_to_access=analytical_platform&"
                 "sort=ascending&"
                 "clear_filter=False&"
@@ -74,7 +72,6 @@ def test_get_context_remove_filter_hrefs(self, search_context, valid_domain):
             "tag-1": (
                 "?query=test&"
                 f"domain={quote(valid_domain.urn)}&"
-                "subdomain=&"
                 "where_to_access=analytical_platform&"
                 "entity_types=TABLE&"
                 "sort=ascending&"
@@ -157,28 +154,3 @@ def test_highlight_results_with_query(self, search_service):
             search_service.results.page_results
             != search_service.highlighted_results.page_results
         )
-
-
-@run_for_dev
-@pytest.mark.parametrize(
-    "domain, subdomain, expected_subdomains",
-    [
-        ("does-not-exist", "", []),
-        (
-            "urn:li:domain:HMPPS",
-            "",
-            [
-                "urn:li:domain:HMPPS",
-                "urn:li:domain:2feb789b-44d3-4412-b998-1f26819fabf9",
-                "urn:li:domain:abe153c1-416b-4abb-be7f-6accf2abb10a",
-            ],
-        ),
-        (
-            "urn:li:domain:HMPPS",
-            "urn:li:domain:2feb789b-44d3-4412-b998-1f26819fabf9",
-            ["urn:li:domain:2feb789b-44d3-4412-b998-1f26819fabf9"],
-        ),
-    ],
-)
-def test_domain_expansion(domain, subdomain, expected_subdomains):
-    assert domains_with_their_subdomains(domain, subdomain) == expected_subdomains