diff --git a/backend/categorisation/categorisation_trigger_request.py b/backend/categorisation/categorisation_trigger_request.py
index 9ef1d106..aa2b8ed3 100644
--- a/backend/categorisation/categorisation_trigger_request.py
+++ b/backend/categorisation/categorisation_trigger_request.py
@@ -1,5 +1,8 @@
+from typing import List, Optional
 from pydantic import BaseModel
 
 
 class CategorisationTriggerRequest(BaseModel):
     portfolio_id: int
+
+    plan_priority_order: Optional[List[int]]
diff --git a/backend/categorisation/processor.py b/backend/categorisation/processor.py
index 97e4c5ad..539f7a68 100644
--- a/backend/categorisation/processor.py
+++ b/backend/categorisation/processor.py
@@ -1,5 +1,5 @@
 from collections import defaultdict
-from typing import Dict, List
+from typing import Dict, List, Optional
 
 from backend.app.db.functions.recommendations_functions import (
     bulk_update_plans,
@@ -14,7 +14,9 @@ from utils.logger import setup_logger
 logger = setup_logger()
 
 
-def process_portfolio(portfolio_id: int) -> None:
+def process_portfolio(
+    portfolio_id: int, plan_priority_order: Optional[List[int]] = []
+) -> None:
     logger.info(f"Processing portfolio {portfolio_id}")
     plans: List[Plan] = _load_plans_for_portfolio(portfolio_id)
     plans_by_property: Dict[int, List[Plan]] = _group_plans_by_property(plans)
@@ -24,7 +26,9 @@ def process_portfolio(portfolio_id: int) -> None:
         if not property_plans:
             raise ValueError(f"No plans for property {uprn}")
 
-        cheapest_plan = _choose_cheapest_relevant_plan(property_plans)
+        cheapest_plan = _choose_cheapest_relevant_plan(
+            property_plans, plan_priority_order
+        )
         _update_default_flags(property_plans, cheapest_plan)
 
 
@@ -64,7 +68,9 @@ def _group_plans_by_property(plans: List[Plan]) -> Dict[int, List[Plan]]:
     return grouped
 
 
-def _choose_cheapest_relevant_plan(plans: List[Plan]) -> Plan:
+def _choose_cheapest_relevant_plan(
+    plans: List[Plan], plan_priority_order: Optional[List[int]] = []
+) -> Plan:
     plans_to_consider: List[Plan] = [p for p in plans if p.is_compliant] or plans
 
     def plan_cost(plan: Plan) -> float:
diff --git a/backend/categorisation/tests/test_prioritised_plan_selected.py b/backend/categorisation/tests/test_prioritised_plan_selected.py
new file mode 100644
index 00000000..03bca666
--- /dev/null
+++ b/backend/categorisation/tests/test_prioritised_plan_selected.py
@@ -0,0 +1,88 @@
+from datetime import datetime
+from typing import List
+import pytest
+
+from backend.app.domain.classes.plan import Plan
+from backend.app.domain.classes.scenario import Scenario
+from backend.app.domain.records.plan_record import PlanRecord
+from backend.app.domain.records.scenario_record import ScenarioRecord
+from backend.app.db.models.portfolio import Epc, PortfolioGoal
+from backend.categorisation.processor import _choose_cheapest_relevant_plan
+
+
+@pytest.fixture
+def created_at_datetime() -> datetime:
+    return datetime.now()
+
+
+@pytest.fixture
+def identical_plan_record(created_at_datetime: datetime, default: bool) -> PlanRecord:
+    return PlanRecord(
+        property_id=1,
+        portfolio_id=1,
+        created_at=created_at_datetime,
+        is_default=default,
+        post_epc_rating=Epc.C,
+        cost_of_works=500.0,
+    )
+
+
+def make_plan_record(created_at_datetime: datetime, default: bool) -> PlanRecord:
+    return PlanRecord(
+        property_id=1,
+        portfolio_id=1,
+        created_at=created_at_datetime,
+        is_default=default,
+        post_epc_rating=Epc.C,
+        cost_of_works=500.0,
+    )
+
+
+def test_prioritised_plan_selected(created_at_datetime: datetime) -> None:
+    # arrange
+    epc_c_scenario_record = ScenarioRecord(
+        name="EPC C",
+        created_at=created_at_datetime,
+        housing_type="",
+        goal=PortfolioGoal.INCREASING_EPC,
+        goal_value="C",
+        trigger_file_path="",
+        multi_plan=False,
+        is_default=True,
+    )
+    epc_c_scenario = Scenario(record=epc_c_scenario_record, id=1)
+    epc_c_plan = Plan(
+        record=make_plan_record(created_at_datetime, True),
+        scenario=epc_c_scenario,
+        id=1,
+    )
+
+    minor_works_scenario_record = ScenarioRecord(
+        name="EPC C - Minor Works",
+        created_at=created_at_datetime,
+        housing_type="",
+        goal=PortfolioGoal.INCREASING_EPC,
+        goal_value="C",
+        trigger_file_path="",
+        multi_plan=False,
+        is_default=False,
+    )
+    minor_works_scenario = Scenario(record=minor_works_scenario_record, id=2)
+    minor_works_plan = Plan(
+        record=make_plan_record(created_at_datetime, False),
+        scenario=minor_works_scenario,
+        id=2,
+    )
+
+    plan_priority_order: List[int] = [2, 1]
+
+    expected_default_plan_id = 2
+
+    # act
+    actual_default_plan = _choose_cheapest_relevant_plan(
+        plans=[epc_c_plan, minor_works_plan],
+        plan_priority_order=plan_priority_order,
+    )
+
+    # assert
+    assert actual_default_plan.id == expected_default_plan_id