diff --git a/db/data/20241114082139_fix_hybrid_beis_dsit_identifier.rb b/db/data/20241114082139_fix_hybrid_beis_dsit_identifier.rb
new file mode 100644
index 000000000..6060533c5
--- /dev/null
+++ b/db/data/20241114082139_fix_hybrid_beis_dsit_identifier.rb
@@ -0,0 +1,67 @@
+# Run me with `rails runner db/data/20241114082139_fix_iati_reporting_org.rb`
+
+# Require me in the console with `require Rails.root + "db/data/20241114082139_fix_hybrid_beis_dsit_identifier.rb"`
+# then run me with `FixHybridBeisDsitIdentifier.new.migrate!`
+#
+# Description:
+#
+# For every Activity where `previous_identifier` is NOT nil
+# When the `previous_identifier` starts "GB-GOV-13" AND `transparency_identifier` starts "GB-GOV-26"
+# Then set `transparency_identifier` to start "GB-GOV-13"
+# AND set `previous_identifier` to nil
+# AND set hybrid_beis_dsit_activity to true.
+#
+class FixHybridBeisDsitIdentifier
+  attr_reader :target, :updated
+
+  def initialize
+    @target = 0
+    @updated = 0
+  end
+
+  def migrate!
+    target_activities.each do |activity|
+      fix_activity(activity)
+    end
+
+    puts "Total target activities: #{@target}"
+    puts "Total updated activities: #{@updated}"
+
+    true
+  end
+
+  def target_activities
+    activities = Activity.where.not(previous_identifier: nil).select do |activity|
+      other_identifier_starts_with_beis(activity.previous_identifier) &&
+        transparency_identifier_starts_with_dsit(activity.transparency_identifier)
+    end
+
+    @target = activities.count
+    activities
+  end
+
+  def fix_activity(activity)
+    puts "Updating activity id #{activity.id} with IATI ID: #{activity.transparency_identifier} and Previous IATI ID: #{activity.previous_identifier}"
+
+    activity.update!(
+      transparency_identifier: activity.previous_identifier,
+      previous_identifier: nil,
+      hybrid_beis_dsit_activity: true
+    )
+
+    @updated += 1
+    puts "Activity Updated!"
+  end
+
+  def other_identifier_starts_with_beis(other_identifier)
+    return if other_identifier.nil?
+
+    other_identifier.slice(0, 9).eql?("GB-GOV-13")
+  end
+
+  def transparency_identifier_starts_with_dsit(transparency_identifier)
+    return if transparency_identifier.nil?
+
+    transparency_identifier.slice(0, 9).eql?("GB-GOV-26")
+  end
+end
diff --git a/spec/db/data/20241114082139_fix_hybrid_beis_dsit_identifier_spec.rb b/spec/db/data/20241114082139_fix_hybrid_beis_dsit_identifier_spec.rb
new file mode 100644
index 000000000..4010781c0
--- /dev/null
+++ b/spec/db/data/20241114082139_fix_hybrid_beis_dsit_identifier_spec.rb
@@ -0,0 +1,98 @@
+require Rails.root + "db/data/20241114082139_fix_hybrid_beis_dsit_identifier.rb"
+
+RSpec.describe FixHybridBeisDsitIdentifier do
+  describe "#migrate!" do
+    it "updates only the appropriate activities and includes a count" do
+      activity_to_update = create(
+        :programme_activity,
+        transparency_identifier: "GB-GOV-26-AAAA-BBBB-CCC-DDDDDDD",
+        previous_identifier: "GB-GOV-13-AAAA-BBBB-CCC-DDDDDDD",
+        hybrid_beis_dsit_activity: false
+      )
+      activity_to_ignore = create(
+        :programme_activity,
+        transparency_identifier: "GB-GOV-26-EEEE-FFFF-GGG-HHHHHHH",
+        previous_identifier: nil,
+        hybrid_beis_dsit_activity: false
+      )
+      other_activity_to_ignore = create(
+        :programme_activity,
+        transparency_identifier: "GB-GOV-13-EEEE-FFFF-GGG-HHHHHHH",
+        previous_identifier: "GB-GOV-13-IIII_JJJJ_KKK_LL",
+        hybrid_beis_dsit_activity: false
+      )
+
+      migration = described_class.new
+      migration.migrate!
+
+      expect(activity_to_update.reload.transparency_identifier).to eql "GB-GOV-13-AAAA-BBBB-CCC-DDDDDDD"
+      expect(activity_to_update.hybrid_beis_dsit_activity).to be true
+
+      expect(activity_to_ignore.reload.transparency_identifier).to eql "GB-GOV-26-EEEE-FFFF-GGG-HHHHHHH"
+      expect(activity_to_ignore.hybrid_beis_dsit_activity).to be false
+
+      expect(other_activity_to_ignore.reload.transparency_identifier).to eql "GB-GOV-13-EEEE-FFFF-GGG-HHHHHHH"
+      expect(other_activity_to_ignore.hybrid_beis_dsit_activity).to be false
+
+      expect(migration.target).to be 1
+      expect(migration.updated).to be 1
+    end
+  end
+
+  describe "#other_identifier_starts_with_beis" do
+    it "returns true for identifiers that start GB-GOV-13" do
+      valid_identifier = "GB-GOV-13-1234-5678-91011"
+
+      expect(described_class.new.other_identifier_starts_with_beis(valid_identifier)).to be true
+    end
+
+    it "returns false for identifiers that do not start GB-GOV-13" do
+      valid_identifier = "GB-GOV-10-1234-5678-91011"
+
+      expect(described_class.new.other_identifier_starts_with_beis(valid_identifier)).to be false
+    end
+  end
+
+  describe "#transparency_identifier_starts_with_dsit" do
+    it "returns true for identifiers that start GB-GOV-26" do
+      valid_identifier = "GB-GOV-26-1234-5678-91011"
+
+      expect(described_class.new.transparency_identifier_starts_with_dsit(valid_identifier)).to be true
+    end
+
+    it "returns false for identifiers that do not start GB-GOV-26" do
+      valid_identifier = "GB-GOV-10-1234-5678-91011"
+
+      expect(described_class.new.transparency_identifier_starts_with_dsit(valid_identifier)).to be false
+    end
+  end
+
+  describe "#fix_activity" do
+    let(:activity) do
+      create(
+        :programme_activity,
+        transparency_identifier: "GB-GOV-26-AAAA-BBBB-CCC-DDDDDDD",
+        previous_identifier: "GB-GOV-13-AAAA-BBBB-CCC-DDDDDDD",
+        hybrid_beis_dsit_activity: false
+      )
+    end
+
+    it "updates the transparency_identifier to the value of previous_identifier" do
+      described_class.new.fix_activity(activity)
+
+      expect(activity.transparency_identifier).to eql "GB-GOV-13-AAAA-BBBB-CCC-DDDDDDD"
+    end
+
+    it "updates the previous_identifier to nil" do
+      described_class.new.fix_activity(activity)
+
+      expect(activity.previous_identifier).to be_nil
+    end
+
+    it "updates the hybrid BEIS DSIT state to true" do
+      described_class.new.fix_activity(activity)
+
+      expect(activity.hybrid_beis_dsit_activity).to be true
+    end
+  end
+end