diff --git a/app/models/derived_variables/lettings_log_variables.rb b/app/models/derived_variables/lettings_log_variables.rb
index d42fb3903..aae49422d 100644
--- a/app/models/derived_variables/lettings_log_variables.rb
+++ b/app/models/derived_variables/lettings_log_variables.rb
@@ -94,6 +94,17 @@ module DerivedVariables::LettingsLogVariables
     self.vacdays = property_vacant_days
 
     set_housingneeds_fields if housingneeds?
+
+    if uprn_known&.zero?
+      self.uprn = nil
+    end
+
+    if uprn_confirmed&.zero?
+      self.uprn = nil
+      self.uprn_known = 0
+    end
+
+    reset_address_fields! if is_supported_housing?
   end
 
 private
@@ -229,4 +240,14 @@ private
     self.housingneeds_g = 0
     self.housingneeds_h = 0
   end
+
+  def reset_address_fields!
+    self.uprn = nil
+    self.uprn_known = nil
+    self.uprn_confirmed = nil
+    self.address_line1 = nil
+    self.address_line2 = nil
+    self.town_or_city = nil
+    self.county = nil
+  end
 end
diff --git a/app/models/lettings_log.rb b/app/models/lettings_log.rb
index 764b23f9a..57281d987 100644
--- a/app/models/lettings_log.rb
+++ b/app/models/lettings_log.rb
@@ -32,6 +32,7 @@ class LettingsLog < Log
   before_validation :reset_location_fields!, unless: :postcode_known?
   before_validation :reset_previous_location_fields!, unless: :previous_postcode_known?
   before_validation :set_derived_fields!
+  after_validation :process_uprn_change!, if: :should_process_uprn_change?
 
   belongs_to :scheme, optional: true
   belongs_to :location, optional: true
@@ -671,4 +672,8 @@ private
   def unknown_housingneeds?
     housingneeds == 3
   end
+
+  def should_process_uprn_change?
+    uprn_changed? && startdate && startdate.year >= 2023
+  end
 end
diff --git a/app/models/log.rb b/app/models/log.rb
index 34c920bd5..3ecc02754 100644
--- a/app/models/log.rb
+++ b/app/models/log.rb
@@ -45,6 +45,7 @@ class Log < ApplicationRecord
       self.address_line2 = presenter.address_line2
       self.town_or_city = presenter.town_or_city
       self.postcode_full = presenter.postcode
+      self.county = nil
       process_postcode_changes!
     end
   end
diff --git a/spec/models/lettings_log_spec.rb b/spec/models/lettings_log_spec.rb
index e2431ff92..44f19c7b7 100644
--- a/spec/models/lettings_log_spec.rb
+++ b/spec/models/lettings_log_spec.rb
@@ -1,6 +1,7 @@
 require "rails_helper"
 require "shared/shared_examples_for_derived_fields"
 
+# rubocop:disable RSpec/AnyInstance
 RSpec.describe LettingsLog do
   let(:different_managing_organisation) { create(:organisation) }
   let(:created_by_user) { create(:user) }
@@ -2995,4 +2996,60 @@ RSpec.describe LettingsLog do
       end
     end
   end
+
+  describe "#process_uprn_change!" do
+    context "when UPRN set to a value" do
+      let(:lettings_log) do
+        create(
+          :lettings_log,
+          uprn: "123456789",
+          uprn_confirmed: 1,
+          county: "county",
+        )
+      end
+
+      it "updates sales log fields" do
+        lettings_log.uprn = "1111111"
+
+        allow_any_instance_of(UprnClient).to receive(:call)
+        allow_any_instance_of(UprnClient).to receive(:result).and_return({
+          "UPRN" => "UPRN",
+          "UDPRN" => "UDPRN",
+          "ADDRESS" => "full address",
+          "SUB_BUILDING_NAME" => "0",
+          "BUILDING_NAME" => "building name",
+          "THOROUGHFARE_NAME" => "thoroughfare",
+          "POST_TOWN" => "posttown",
+          "POSTCODE" => "postcode",
+        })
+
+        expect { lettings_log.process_uprn_change! }.to change(lettings_log, :address_line1).from(nil).to("0, Building Name, Thoroughfare")
+        .and change(lettings_log, :town_or_city).from(nil).to("Posttown")
+        .and change(lettings_log, :postcode_full).from(nil).to("POSTCODE")
+        .and change(lettings_log, :uprn_confirmed).from(1).to(nil)
+        .and change(lettings_log, :county).from("county").to(nil)
+      end
+    end
+
+    context "when UPRN nil" do
+      let(:lettings_log) { create(:lettings_log, uprn: nil) }
+
+      it "does not update sales log" do
+        expect { lettings_log.process_uprn_change! }.not_to change(lettings_log, :attributes)
+      end
+    end
+
+    context "when service errors" do
+      let(:lettings_log) { create(:lettings_log, uprn: "123456789", uprn_confirmed: 1) }
+      let(:error_message) { "error" }
+
+      it "adds error to sales log" do
+        allow_any_instance_of(UprnClient).to receive(:call)
+        allow_any_instance_of(UprnClient).to receive(:error).and_return(error_message)
+
+        expect { lettings_log.process_uprn_change! }.to change { lettings_log.errors[:uprn] }.from([]).to([error_message])
+      end
+    end
+  end
 end
+# rubocop:enable RSpec/AnyInstance
diff --git a/spec/models/sales_log_spec.rb b/spec/models/sales_log_spec.rb
index 7f6c74fc4..9b3d82bf5 100644
--- a/spec/models/sales_log_spec.rb
+++ b/spec/models/sales_log_spec.rb
@@ -511,7 +511,14 @@ RSpec.describe SalesLog, type: :model do
 
   describe "#process_uprn_change!" do
     context "when UPRN set to a value" do
-      let(:sales_log) { create(:sales_log, uprn: "123456789", uprn_confirmed: 1) }
+      let(:sales_log) do
+        create(
+          :sales_log,
+          uprn: "123456789",
+          uprn_confirmed: 1,
+          county: "county",
+        )
+      end
 
       it "updates sales log fields" do
         sales_log.uprn = "1111111"
@@ -532,6 +539,7 @@ RSpec.describe SalesLog, type: :model do
         .and change(sales_log, :town_or_city).from(nil).to("Posttown")
         .and change(sales_log, :postcode_full).from(nil).to("POSTCODE")
         .and change(sales_log, :uprn_confirmed).from(1).to(nil)
+        .and change(sales_log, :county).from("county").to(nil)
       end
     end