diff --git a/app/helpers/schemes_helper.rb b/app/helpers/schemes_helper.rb
index 0e318d283..1133d201c 100644
--- a/app/helpers/schemes_helper.rb
+++ b/app/helpers/schemes_helper.rb
@@ -85,6 +85,13 @@ module SchemesHelper
     end
   end
 
+  def display_duplicate_schemes_banner?(organisation, current_user)
+    return unless organisation.absorbed_organisations.merged_during_open_collection_period.any?
+    return unless current_user.data_coordinator? || current_user.support?
+
+    organisation.owned_schemes.duplicate_sets.any? || organisation.owned_schemes.any? { |scheme| scheme.locations.duplicate_sets.any? }
+  end
+
 private
 
   ActivePeriod = Struct.new(:from, :to)
diff --git a/spec/helpers/schemes_helper_spec.rb b/spec/helpers/schemes_helper_spec.rb
index 0df032c3f..0a37a1b38 100644
--- a/spec/helpers/schemes_helper_spec.rb
+++ b/spec/helpers/schemes_helper_spec.rb
@@ -118,4 +118,101 @@ RSpec.describe SchemesHelper do
       end
     end
   end
+
+  describe "display_duplicate_schemes_banner?" do
+    let(:organisation) { create(:organisation) }
+    let(:current_user) { create(:user, :support) }
+
+    context "when organisation has not absorbed other organisations" do
+      context "and it has duplicate schemes" do
+        before do
+          create_list(:scheme, 2, :duplicate, owning_organisation: organisation)
+        end
+
+        it "does not display the banner" do
+          expect(display_duplicate_schemes_banner?(organisation, current_user)).to be_falsey
+        end
+      end
+    end
+
+    context "when organisation has absorbed other organisations in open collection year" do
+      before do
+        build(:organisation, merge_date: Time.zone.today, absorbing_organisation_id: organisation.id).save(validate: false)
+      end
+
+      context "and it has duplicate schemes" do
+        before do
+          create_list(:scheme, 2, :duplicate, owning_organisation: organisation)
+        end
+
+        it "displays the banner" do
+          expect(display_duplicate_schemes_banner?(organisation, current_user)).to be_truthy
+        end
+      end
+
+      context "and it has duplicate locations" do
+        let(:scheme) { create(:scheme, owning_organisation: organisation) }
+
+        before do
+          create_list(:location, 2, postcode: "AB1 2CD", mobility_type: "A", scheme:)
+        end
+
+        it "displays the banner" do
+          expect(display_duplicate_schemes_banner?(organisation, current_user)).to be_truthy
+        end
+      end
+
+      context "and it has no duplicate schemes or locations" do
+        it "does not display the banner" do
+          expect(display_duplicate_schemes_banner?(organisation, current_user)).to be_falsey
+        end
+      end
+
+      context "and it is viewed by data provider" do
+        let(:current_user) { create(:user, :data_provider) }
+
+        before do
+          create_list(:scheme, 2, :duplicate, owning_organisation: organisation)
+        end
+
+        it "does not display the banner" do
+          expect(display_duplicate_schemes_banner?(organisation, current_user)).to be_falsey
+        end
+      end
+    end
+
+    context "when organisation has absorbed other organisations in closed collection year" do
+      before do
+        build(:organisation, merge_date: Time.zone.today - 2.years, absorbing_organisation_id: organisation.id).save(validate: false)
+      end
+
+      context "and it has duplicate schemes" do
+        before do
+          create_list(:scheme, 2, :duplicate, owning_organisation: organisation)
+        end
+
+        it "does not display the banner" do
+          expect(display_duplicate_schemes_banner?(organisation, current_user)).to be_falsey
+        end
+      end
+
+      context "and it has duplicate locations" do
+        let(:scheme) { create(:scheme, owning_organisation: organisation) }
+
+        before do
+          create(:location, postcode: "AB1 2CD", mobility_type: "A", scheme:)
+        end
+
+        it "does not display the banner" do
+          expect(display_duplicate_schemes_banner?(organisation, current_user)).to be_falsey
+        end
+      end
+
+      context "and it has no duplicate schemes or locations" do
+        it "does not display the banner" do
+          expect(display_duplicate_schemes_banner?(organisation, current_user)).to be_falsey
+        end
+      end
+    end
+  end
 end