diff --git a/app/models/__init__.py b/app/models/__init__.py
index b77f2b26df..6709e8831d 100644
--- a/app/models/__init__.py
+++ b/app/models/__init__.py
@@ -14,7 +14,7 @@ class JSONModelMeta(SerialisedModelMeta, ABCMeta):
 
 
 @total_ordering
-class JSONModel(SerialisedModel, ABC, metaclass=JSONModelMeta):
+class StrictJSONModel(SerialisedModel, ABC, metaclass=JSONModelMeta):
     @property
     @abstractmethod
     def __sort_attribute__(self):
@@ -43,6 +43,14 @@ def __eq__(self, other):
     def __hash__(self):
         return hash(self.id)
 
+    def _get_by_id(self, things, id):
+        try:
+            return next(thing for thing in things if thing["id"] == str(id))
+        except StopIteration:
+            abort(404)
+
+
+class JSONModel(StrictJSONModel):
     def __init__(self, _dict):
         # in the case of a bad request _dict may be `None`
         self._dict = _dict or {}
@@ -54,12 +62,6 @@ def __init__(self, _dict):
     def __bool__(self):
         return self._dict != {}
 
-    def _get_by_id(self, things, id):
-        try:
-            return next(thing for thing in things if thing["id"] == str(id))
-        except StopIteration:
-            abort(404)
-
 
 class ModelList(SerialisedModelCollection):
     @property
diff --git a/app/models/api_key.py b/app/models/api_key.py
index 8f279b60f8..83b9fac075 100644
--- a/app/models/api_key.py
+++ b/app/models/api_key.py
@@ -3,11 +3,11 @@
 
 from flask import abort
 
-from app.models import JSONModel, ModelList
+from app.models import ModelList, StrictJSONModel
 from app.notify_client.api_key_api_client import api_key_api_client
 
 
-class APIKey(JSONModel):
+class APIKey(StrictJSONModel):
     created_at: datetime
     created_by: Any
     expiry_date: datetime
diff --git a/app/models/contact_list.py b/app/models/contact_list.py
index 5e29142c88..365f37e272 100644
--- a/app/models/contact_list.py
+++ b/app/models/contact_list.py
@@ -8,7 +8,7 @@
 from notifications_utils.recipients import RecipientCSV
 from werkzeug.utils import cached_property
 
-from app.models import JSONModel, ModelList
+from app.models import ModelList, StrictJSONModel
 from app.models.job import PaginatedJobsAndScheduledJobs
 from app.notify_client.contact_list_api_client import contact_list_api_client
 from app.s3_client.s3_csv_client import (
@@ -20,7 +20,7 @@
 from app.utils.templates import get_sample_template
 
 
-class ContactList(JSONModel):
+class ContactList(StrictJSONModel):
     id: Any
     created_at: datetime
     created_by: Any
diff --git a/app/models/letter_rates.py b/app/models/letter_rates.py
index c33d25b00f..39c85e2ea9 100644
--- a/app/models/letter_rates.py
+++ b/app/models/letter_rates.py
@@ -1,11 +1,11 @@
 from datetime import datetime
 from typing import Any
 
-from app.models import JSONModel, ModelList
+from app.models import ModelList, StrictJSONModel
 from app.notify_client.letter_rate_api_client import letter_rate_api_client
 
 
-class LetterRate(JSONModel):
+class LetterRate(StrictJSONModel):
     sheet_count: int
     rate: float
     post_class: Any
diff --git a/app/models/report_request.py b/app/models/report_request.py
index c488e6bb73..55b58ba909 100644
--- a/app/models/report_request.py
+++ b/app/models/report_request.py
@@ -5,11 +5,11 @@
 from notifications_utils.s3 import s3download
 
 from app import report_request_api_client
-from app.models import JSONModel
+from app.models import StrictJSONModel
 from app.s3_client import check_s3_object_exists
 
 
-class ReportRequest(JSONModel):
+class ReportRequest(StrictJSONModel):
     id: Any
     user_id: Any
     service_id: Any
diff --git a/app/models/service.py b/app/models/service.py
index 1913d525df..e6a00e3657 100644
--- a/app/models/service.py
+++ b/app/models/service.py
@@ -13,7 +13,7 @@
     SIGN_IN_METHOD_TEXT,
     SIGN_IN_METHOD_TEXT_OR_EMAIL,
 )
-from app.models import JSONModel
+from app.models import JSONModel, StrictJSONModel
 from app.models.api_key import APIKeys
 from app.models.branding import EmailBranding, LetterBranding
 from app.models.contact_list import ContactLists
@@ -680,7 +680,7 @@ class Services(SerialisedModelCollection):
     model = Service
 
 
-class ServiceJoinRequest(JSONModel):
+class ServiceJoinRequest(StrictJSONModel):
     id: Any
     requester: Any
     service_id: Any
@@ -690,8 +690,6 @@ class ServiceJoinRequest(JSONModel):
     reason: str
     status: str
     contacted_service_users: list[str]
-    requested_service: Any
-    permissions: list[str]
 
     __sort_attribute__ = "id"
 
diff --git a/app/models/sms_rate.py b/app/models/sms_rate.py
index 015955a7b2..3d4f67b471 100644
--- a/app/models/sms_rate.py
+++ b/app/models/sms_rate.py
@@ -1,11 +1,11 @@
 from datetime import datetime
 
 from app.formatters import format_pennies_as_currency
-from app.models import JSONModel
+from app.models import StrictJSONModel
 from app.notify_client.sms_rate_client import sms_rate_api_client
 
 
-class SMSRate(JSONModel):
+class SMSRate(StrictJSONModel):
     rate: float
     valid_from: datetime
 
diff --git a/tests/__init__.py b/tests/__init__.py
index 18d6374a62..0c4465c41f 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -375,8 +375,15 @@ def template_version_json(service_id, id_, created_by, version=1, created_at=Non
     return template
 
 
-def api_key_json(id_, name, expiry_date=None, key_type="normal"):
-    return {"id": id_, "name": name, "expiry_date": expiry_date, "key_type": key_type}
+def api_key_json(id_, name, expiry_date=None, created_at=None, created_by=None, key_type="normal"):
+    return {
+        "id": id_,
+        "name": name,
+        "expiry_date": expiry_date,
+        "key_type": key_type,
+        "created_at": created_at,
+        "created_by": created_by,
+    }
 
 
 def invite_json(
diff --git a/tests/app/main/forms/test_create_key_form.py b/tests/app/main/forms/test_create_key_form.py
index b7ea82b3af..3e9b412e36 100644
--- a/tests/app/main/forms/test_create_key_form.py
+++ b/tests/app/main/forms/test_create_key_form.py
@@ -1,8 +1,11 @@
+from uuid import uuid4
+
 import pytest
 from werkzeug.datastructures import MultiDict
 
 from app.main.forms import CreateKeyForm
 from app.models.api_key import APIKeys
+from tests import api_key_json
 
 
 @pytest.mark.parametrize(
@@ -22,14 +25,16 @@ def test_return_validation_error_when_key_name_exists(
         "app.models.api_key.api_key_api_client.get_api_keys",
         return_value={
             "apiKeys": [
-                {
-                    "name": "some key",
-                    "expiry_date": expiry_date,
-                },
-                {
-                    "name": "another key",
-                    "expiry_date": None,
-                },
+                api_key_json(
+                    id_=str(uuid4()),
+                    name="some key",
+                    expiry_date=expiry_date,
+                ),
+                api_key_json(
+                    id_=str(uuid4()),
+                    name="another key",
+                    expiry_date=None,
+                ),
             ]
         },
     )
diff --git a/tests/app/models/test_base_model.py b/tests/app/models/test_base_model.py
index 06eff72b67..8cff6876fb 100644
--- a/tests/app/models/test_base_model.py
+++ b/tests/app/models/test_base_model.py
@@ -1,6 +1,6 @@
 import pytest
 
-from app.models import JSONModel
+from app.models import JSONModel, StrictJSONModel
 
 
 def test_looks_up_from_dict():
@@ -58,6 +58,17 @@ class Custom(JSONModel):
     assert str(e.value) == "'Custom' object has no attribute 'foo'"
 
 
+def test_strict_model_raises_keyerror_if_item_missing_from_dict_on_instantiation():
+    class Custom(StrictJSONModel):
+        foo: str
+        __sort_attribute__ = "foo"
+
+    with pytest.raises(KeyError) as e:
+        Custom({})
+
+    assert str(e.value) == "'foo'"
+
+
 @pytest.mark.parametrize(
     "json_response",
     (
diff --git a/tests/app/models/test_contact_list.py b/tests/app/models/test_contact_list.py
index 0b9d8ec79b..e3c2e3cfa1 100644
--- a/tests/app/models/test_contact_list.py
+++ b/tests/app/models/test_contact_list.py
@@ -1,9 +1,10 @@
 from app.models.contact_list import ContactList
 from app.models.job import PaginatedJobs
+from tests import contact_list_json
 
 
 def test_get_jobs(mock_get_jobs):
-    contact_list = ContactList({"id": "a", "service_id": "b"})
+    contact_list = ContactList(contact_list_json(id_="a", service_id="b"))
     assert isinstance(contact_list.get_jobs(page=123), PaginatedJobs)
     # mock_get_jobs mocks the underlying API client method, not
     # contact_list.get_jobs
diff --git a/tests/conftest.py b/tests/conftest.py
index 9cd5cbc1cc..d313b66b06 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1909,13 +1909,13 @@ def _create(
         row_count,
         template_type,
     ):
-        return {
-            "service_id": service_id,
-            "upload_id": upload_id,
-            "original_file_name": original_file_name,
-            "row_count": row_count,
-            "template_type": template_type,
-        }
+        return contact_list_json(
+            id_=upload_id,
+            service_id=service_id,
+            original_file_name=original_file_name,
+            row_count=row_count,
+            template_type=template_type,
+        )
 
     return mocker.patch(
         "app.contact_list_api_client.create_contact_list",