diff --git a/app/models/derived_variables/lettings_log_variables.rb b/app/models/derived_variables/lettings_log_variables.rb
index fb174a9c1..d0aab14cb 100644
--- a/app/models/derived_variables/lettings_log_variables.rb
+++ b/app/models/derived_variables/lettings_log_variables.rb
@@ -115,6 +115,8 @@ module DerivedVariables::LettingsLogVariables
       self.uprn_known = 0
     end
 
+    self.nationality_all = nationality_all_group if nationality_uk_or_prefers_not_to_say?
+
     reset_address_fields! if is_supported_housing?
   end
 
diff --git a/app/models/derived_variables/sales_log_variables.rb b/app/models/derived_variables/sales_log_variables.rb
index 6532b228f..12d860492 100644
--- a/app/models/derived_variables/sales_log_variables.rb
+++ b/app/models/derived_variables/sales_log_variables.rb
@@ -35,6 +35,9 @@ module DerivedVariables::SalesLogVariables
       self.uprn_known = 0
     end
 
+    self.nationality_all = nationality_all_group if nationality_uk_or_prefers_not_to_say?
+    self.nationality_all_buyer2 = nationality_all_buyer2_group if nationality2_uk_or_prefers_not_to_say?
+
     set_encoded_derived_values!(DEPENDENCIES)
   end
 
diff --git a/app/models/log.rb b/app/models/log.rb
index 8814e771d..5de8b924c 100644
--- a/app/models/log.rb
+++ b/app/models/log.rb
@@ -209,6 +209,10 @@ class Log < ApplicationRecord
     end
   end
 
+  def nationality_uk_or_prefers_not_to_say?
+    nationality_all_group == 13 || nationality_all_group == 826
+  end
+
 private
 
   # Handle logs that are older than previous collection start date
diff --git a/app/models/sales_log.rb b/app/models/sales_log.rb
index 5acd409de..1591e4a14 100644
--- a/app/models/sales_log.rb
+++ b/app/models/sales_log.rb
@@ -473,4 +473,8 @@ class SalesLog < Log
   def duplicates
     SalesLog.where.not(duplicate_set_id: nil).where(duplicate_set_id:).where.not(id:)
   end
+
+  def nationality2_uk_or_prefers_not_to_say?
+    nationality_all_buyer2_group == 13 || nationality_all_buyer2_group == 826
+  end
 end
diff --git a/spec/models/lettings_log_spec.rb b/spec/models/lettings_log_spec.rb
index f2bbbe4be..7d2fcc8c2 100644
--- a/spec/models/lettings_log_spec.rb
+++ b/spec/models/lettings_log_spec.rb
@@ -2330,6 +2330,43 @@ RSpec.describe LettingsLog do
         expect(record_from_db["irproduct"]).to eq(nil)
       end
     end
+
+    context "when updating nationality_all_group" do
+      let!(:lettings_log) do
+        described_class.create({
+          managing_organisation: owning_organisation,
+          owning_organisation:,
+          created_by: created_by_user,
+          startdate: Time.zone.local(2024, 4, 10),
+          needstype: 1,
+          renewal: 1,
+          rent_type: 1,
+        })
+      end
+
+      before do
+        Timecop.freeze(Time.zone.local(2024, 4, 10))
+        Singleton.__init__(FormHandler)
+      end
+
+      after do
+        Timecop.return
+        Singleton.__init__(FormHandler)
+      end
+
+      it "correctly derives nationality_all when it's UK" do
+        expect { lettings_log.update!(nationality_all_group: 826, declaration: 1) }.to change(lettings_log, :nationality_all).to 826
+      end
+
+      it "correctly derives nationality_all when it's prefers not to say" do
+        expect { lettings_log.update!(nationality_all_group: 13, declaration: 1) }.to change(lettings_log, :nationality_all).to 13
+      end
+
+      it "does not derive nationality_all when it's other or not given" do
+        expect { lettings_log.update!(nationality_all_group: 12, declaration: 1) }.not_to change(lettings_log, :nationality_all)
+        expect { lettings_log.update!(nationality_all_group: nil, declaration: 1) }.not_to change(lettings_log, :nationality_all)
+      end
+    end
   end
 
   describe "optional fields" do
diff --git a/spec/models/sales_log_spec.rb b/spec/models/sales_log_spec.rb
index edaf4b60a..87c9b32f4 100644
--- a/spec/models/sales_log_spec.rb
+++ b/spec/models/sales_log_spec.rb
@@ -577,6 +577,25 @@ RSpec.describe SalesLog, type: :model do
         end
       end
     end
+
+    context "when deriving nationality variables" do
+      it "correctly derives nationality_all/nationality_all_buyer2 when it's UK" do
+        expect { sales_log.update!(nationality_all_group: 826) }.to change(sales_log, :nationality_all).to 826
+        expect { sales_log.update!(nationality_all_buyer2_group: 826) }.to change(sales_log, :nationality_all_buyer2).to 826
+      end
+
+      it "correctly derives nationality_all/nationality_all_buyer2 when buyer prefers not to say" do
+        expect { sales_log.update!(nationality_all_group: 13) }.to change(sales_log, :nationality_all).to 13
+        expect { sales_log.update!(nationality_all_buyer2_group: 13) }.to change(sales_log, :nationality_all_buyer2).to 13
+      end
+
+      it "does not derive nationality_all/nationality_all_buyer2 when it is other or not given" do
+        expect { sales_log.update!(nationality_all_group: 12) }.not_to change(sales_log, :nationality_all)
+        expect { sales_log.update!(nationality_all_buyer2_group: 12) }.not_to change(sales_log, :nationality_all_buyer2)
+        expect { sales_log.update!(nationality_all_group: nil) }.not_to change(sales_log, :nationality_all)
+        expect { sales_log.update!(nationality_all_buyer2_group: nil) }.not_to change(sales_log, :nationality_all_buyer2)
+      end
+    end
   end
 
   context "when saving addresses" do