diff --git a/app/models/case_log.rb b/app/models/case_log.rb
index 066d9450c..79fb9ffb6 100644
--- a/app/models/case_log.rb
+++ b/app/models/case_log.rb
@@ -227,6 +227,10 @@ class CaseLog < ApplicationRecord
     prevten == 21
   end
 
+  def is_reason_permanently_decanted?
+    reason == 1
+  end
+
 private
 
   PIO = Postcodes::IO.new
diff --git a/app/models/validations/household_validations.rb b/app/models/validations/household_validations.rb
index 3f410a007..67688794f 100644
--- a/app/models/validations/household_validations.rb
+++ b/app/models/validations/household_validations.rb
@@ -19,6 +19,11 @@ module Validations::HouseholdValidations
       record.errors.add :reason, I18n.t("validations.household.underoccupation_benefitcap.dont_know_required")
     end
     validate_other_field(record, 31, :reason, :other_reason_for_leaving_last_settled_home)
+
+    if record.is_reason_permanently_decanted? && record.referral.present? && !record.is_internal_transfer?
+      record.errors.add :referral, I18n.t("validations.household.referral.reason_permanently_decanted")
+      record.errors.add :reason, I18n.t("validations.household.reason.not_internal_transfer")
+    end
   end
 
   def validate_armed_forces(record)
diff --git a/config/locales/en.yml b/config/locales/en.yml
index f73a277cd..a11768129 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -132,6 +132,7 @@ en:
         assessed_homeless: "Answer cannot be internal transfer as you already told us the tenant was assessed as homeless"
         other_homeless: "Answer cannot be internal transfer as you already told us the tenant was considered homeless by their landlord"
         prevten_invalid: "Answer cannot be internal transfer as you already told us the source of referral for this letting was %{prevten}"
+        reason_permanently_decanted: "Answer must be internal transfer as you already told us the tenant was permanently decanted from another property owned by this landlord"
       homeless:
         assessed:
           internal_transfer: "Answer cannot be assessed as homeless as you already told us this tenancy is an internal transfer"
@@ -142,6 +143,8 @@ en:
       previous_la_known: "Enter a local authority"
       gender:
         male_refuge: "Answer cannot be refuge as the lead tenant identifies as male"
+      reason:
+        not_internal_transfer: "Answer cannot be permanently decanted from another property owned by this landlord as you told us the source of referral for this tenancy was not an internal transfer"
 
     tenancy:
       length:
diff --git a/spec/models/validations/household_validations_spec.rb b/spec/models/validations/household_validations_spec.rb
index b07e6adbb..b8a2dba23 100644
--- a/spec/models/validations/household_validations_spec.rb
+++ b/spec/models/validations/household_validations_spec.rb
@@ -229,6 +229,30 @@ RSpec.describe Validations::HouseholdValidations do
         expect(record.errors["reason"]).to be_empty
       end
     end
+
+    context "when referral is not internal transfer" do
+      it "cannot be permanently decanted from another property owned by this landlord" do
+        record.reason = 1
+        record.referral = 2
+        household_validator.validate_reason_for_leaving_last_settled_home(record)
+        expect(record.errors["reason"])
+          .to include(match(I18n.t("validations.household.reason.not_internal_transfer")))
+        expect(record.errors["referral"])
+          .to include(match(I18n.t("validations.household.referral.reason_permanently_decanted")))
+      end
+    end
+
+    context "when referral is internal transfer" do
+      it "can be permanently decanted from another property owned by this landlord" do
+        record.reason = 1
+        record.referral = 1
+        household_validator.validate_reason_for_leaving_last_settled_home(record)
+        expect(record.errors["reason"])
+          .to be_empty
+        expect(record.errors["referral"])
+          .to be_empty
+      end
+    end
   end
 
   describe "armed forces validations" do