diff --git a/app/services/imports/lettings_logs_field_import_service.rb b/app/services/imports/lettings_logs_field_import_service.rb
index f69fe5792..c7044a062 100644
--- a/app/services/imports/lettings_logs_field_import_service.rb
+++ b/app/services/imports/lettings_logs_field_import_service.rb
@@ -20,6 +20,8 @@ module Imports
         import_from(folder, :update_homelessness)
       when "created_by"
         import_from(folder, :update_created_by)
+      when "sex_and_relat"
+        import_from(folder, :update_sex_and_relat)
       else
         raise "Updating #{field} is not supported by the field import service"
       end
@@ -249,5 +251,31 @@ module Imports
       log_import_service.send(:create_log, xml_doc)
       @logger.info("lettings log \"#{record.old_id}\" has been reimported with id #{record.id}")
     end
+
+    def update_sex_and_relat(xml_doc)
+      return if meta_field_value(xml_doc, "form-name").include?("Sales")
+
+      old_id = meta_field_value(xml_doc, "document-id")
+      record = LettingsLog.find_by(old_id:)
+
+      return @logger.warn("lettings log with old id #{old_id} not found") unless record
+
+      return @logger.info("lettings log #{record.id} has values for sex2 and relat2, skipping update") if record.sex2 && record.relat2
+      return @logger.info("lettings log #{record.id} has no hhmemb value, skipping update") if record.hhmemb.blank?
+      return @logger.info("lettings log #{record.id} has value 'no' for details_known2, skipping update") if record.details_known_2 == 1
+
+      if record.sex2.blank?
+        record.sex2 = sex(xml_doc, 2)
+        @logger.info("lettings log #{record.id}'s sex2 value has been set to #{record.sex2}")
+      end
+
+      if record.relat2.blank?
+        record.relat2 = relat(xml_doc, 2)
+        @logger.info("lettings log #{record.id}'s relat2 value has been set to #{record.relat2}")
+      end
+
+      record.values_updated_at = Time.zone.now
+      record.save!
+    end
   end
 end
diff --git a/spec/services/imports/lettings_logs_field_import_service_spec.rb b/spec/services/imports/lettings_logs_field_import_service_spec.rb
index 669482b8a..6985200b9 100644
--- a/spec/services/imports/lettings_logs_field_import_service_spec.rb
+++ b/spec/services/imports/lettings_logs_field_import_service_spec.rb
@@ -779,4 +779,103 @@ RSpec.describe Imports::LettingsLogsFieldImportService do
       end
     end
   end
+
+  context "when updating sex_and_relat" do
+    let(:field) { "sex_and_relat" }
+    let(:lettings_log) { LettingsLog.find_by(old_id: lettings_log_id) }
+
+    before do
+      Imports::LettingsLogsImportService.new(storage_service, logger).create_logs(fixture_directory)
+      lettings_log_file.rewind
+      lettings_log_xml.at_xpath("//xmlns:P2Sex").content = "Person prefers not to say"
+      lettings_log_xml.at_xpath("//xmlns:P2Rel").content = "Person prefers not to say"
+    end
+
+    context "when the lettings log has no sex or relat value" do
+      before do
+        lettings_log.update!(sex2: nil, relat2: nil, details_known_2: 0, values_updated_at: nil)
+      end
+
+      it "updates the lettings_log sex and relat value if details for person are known" do
+        expect(logger).to receive(:info).with(/lettings log \d+'s sex2 value has been set to R/)
+        expect(logger).to receive(:info).with(/lettings log \d+'s relat2 value has been set to R/)
+        import_service.send(:update_sex_and_relat, lettings_log_xml)
+        lettings_log.reload
+        expect(lettings_log.sex2).to eq("R")
+        expect(lettings_log.relat2).to eq("R")
+        expect(lettings_log.values_updated_at).not_to be_nil
+      end
+
+      it "does not update the lettings_log sex and relat value if details for person are not known" do
+        lettings_log.update!(details_known_2: 1)
+
+        expect(logger).to receive(:info).with(/lettings log \d+ has value 'no' for details_known2, skipping update/)
+        import_service.send(:update_sex_and_relat, lettings_log_xml)
+        lettings_log.reload
+        expect(lettings_log.sex2).to eq(nil)
+        expect(lettings_log.relat2).to eq(nil)
+        expect(lettings_log.values_updated_at).to be_nil
+      end
+    end
+
+    context "when the lettings log has sex and relat value" do
+      before do
+        lettings_log.update!(sex2: "F", relat2: "R", details_known_2: 0, values_updated_at: nil)
+      end
+
+      it "does not update the lettings_log sex and relat values" do
+        expect(logger).to receive(:info).with(/lettings log \d+ has values for sex2 and relat2, skipping update/)
+        import_service.send(:update_sex_and_relat, lettings_log_xml)
+        lettings_log.reload
+        expect(lettings_log.sex2).to eq("F")
+        expect(lettings_log.relat2).to eq("R")
+        expect(lettings_log.values_updated_at).to be_nil
+      end
+    end
+
+    context "when the lettings log has sex value" do
+      before do
+        lettings_log.update!(sex2: "F", relat2: nil, details_known_2: 0, values_updated_at: nil)
+      end
+
+      it "only updates relat value" do
+        expect(logger).to receive(:info).with(/lettings log \d+'s relat2 value has been set to R/)
+        import_service.send(:update_sex_and_relat, lettings_log_xml)
+        lettings_log.reload
+        expect(lettings_log.sex2).to eq("F")
+        expect(lettings_log.relat2).to eq("R")
+        expect(lettings_log.values_updated_at).not_to be_nil
+      end
+    end
+
+    context "when the lettings log has relat value" do
+      before do
+        lettings_log.update!(sex2: nil, relat2: "X", details_known_2: 0, values_updated_at: nil)
+      end
+
+      it "only updates sex value" do
+        expect(logger).to receive(:info).with(/lettings log \d+'s sex2 value has been set to R/)
+        import_service.send(:update_sex_and_relat, lettings_log_xml)
+        lettings_log.reload
+        expect(lettings_log.sex2).to eq("R")
+        expect(lettings_log.relat2).to eq("X")
+        expect(lettings_log.values_updated_at).not_to be_nil
+      end
+    end
+
+    context "when the lettings log has no hhmemb value" do
+      before do
+        lettings_log.update!(sex2: nil, relat2: nil, hhmemb: nil, values_updated_at: nil)
+      end
+
+      it "does not update the lettings_log sex and relat values" do
+        expect(logger).to receive(:info).with(/lettings log \d+ has no hhmemb value, skipping update/)
+        import_service.send(:update_sex_and_relat, lettings_log_xml)
+        lettings_log.reload
+        expect(lettings_log.sex2).to eq(nil)
+        expect(lettings_log.relat2).to eq(nil)
+        expect(lettings_log.values_updated_at).to be_nil
+      end
+    end
+  end
 end