diff --git a/app/controllers/organisation_relationships_controller.rb b/app/controllers/organisation_relationships_controller.rb
index 29c572f62..53952d3d6 100644
--- a/app/controllers/organisation_relationships_controller.rb
+++ b/app/controllers/organisation_relationships_controller.rb
@@ -29,22 +29,24 @@ class OrganisationRelationshipsController < ApplicationController
 
   def add_housing_provider
     @organisations = Organisation.where.not(id: @organisation.id).pluck(:id, :name)
+    @organisation_relationship = OrganisationRelationship.new
     respond_to :html
   end
 
   def add_managing_agent
     @organisations = Organisation.where.not(id: @organisation.id).pluck(:id, :name)
+    @organisation_relationship = OrganisationRelationship.new
     respond_to :html
   end
 
   def create_housing_provider
     child_organisation = @organisation
-    if params[:organisation_relationship].present? && params[:organisation_relationship][:related_organisation_id].present?
-      parent_organisation = related_organisation
+    if params[:organisation_relationship].present? && params[:organisation_relationship][:parent_organisation_id].present?
+      parent_organisation = @parent_organisation ||= Organisation.find(params[:organisation_relationship][:parent_organisation_id])
     end
     @organisation_relationship = OrganisationRelationship.new(child_organisation:, parent_organisation:)
     if @organisation_relationship.save(context: :housing_provider)
-      flash[:notice] = "#{related_organisation.name} is now one of #{current_user.data_coordinator? ? 'your' : "this organisation's"} housing providers"
+      flash[:notice] = "#{parent_organisation.name} is now one of #{current_user.data_coordinator? ? 'your' : "this organisation's"} housing providers"
       redirect_to housing_providers_organisation_path
     else
       @organisations = Organisation.where.not(id: child_organisation.id).pluck(:id, :name)
@@ -54,12 +56,12 @@ class OrganisationRelationshipsController < ApplicationController
 
   def create_managing_agent
     parent_organisation = @organisation
-    if params[:organisation_relationship].present? && params[:organisation_relationship][:related_organisation_id].present?
-      child_organisation = related_organisation
+    if params[:organisation_relationship].present? && params[:organisation_relationship][:child_organisation_id].present?
+      child_organisation = @child_organisation ||= Organisation.find(params[:organisation_relationship][:child_organisation_id])
     end
     @organisation_relationship = OrganisationRelationship.new(child_organisation:, parent_organisation:)
     if @organisation_relationship.save(context: :managing_agent)
-      flash[:notice] = "#{related_organisation.name} is now one of #{current_user.data_coordinator? ? 'your' : "this organisation's"} managing agents"
+      flash[:notice] = "#{child_organisation.name} is now one of #{current_user.data_coordinator? ? 'your' : "this organisation's"} managing agents"
       redirect_to managing_agents_organisation_path
     else
       @organisations = Organisation.where.not(id: parent_organisation.id).pluck(:id, :name)
@@ -97,19 +99,10 @@ class OrganisationRelationshipsController < ApplicationController
 
 private
 
-  def create!(child_organisation:, parent_organisation:)
-    @resource = OrganisationRelationship.new(child_organisation:, parent_organisation:)
-    @resource.save!
-  end
-
   def organisation
     @organisation ||= Organisation.find(params[:id])
   end
 
-  def related_organisation
-    @related_organisation ||= Organisation.find(params[:organisation_relationship][:related_organisation_id])
-  end
-
   def target_organisation
     @target_organisation ||= Organisation.find(params[:target_organisation_id])
   end
diff --git a/app/models/organisation_relationship.rb b/app/models/organisation_relationship.rb
index 72f74cbb9..bf936f408 100644
--- a/app/models/organisation_relationship.rb
+++ b/app/models/organisation_relationship.rb
@@ -1,26 +1,17 @@
 class OrganisationRelationship < ApplicationRecord
   belongs_to :child_organisation, class_name: "Organisation"
   belongs_to :parent_organisation, class_name: "Organisation"
-  validate :validate_housing_provider_relationship, on: :housing_provider
-  validate :validate_managing_agent_relationship, on: :managing_agent
+  validates :parent_organisation_id, presence: { message: "You must choose a housing provider" }, on: :housing_provider
+  validates :child_organisation_id, presence: { message: "You must choose a managing agent" }, on: :managing_agent
+  validates :parent_organisation_id, uniqueness: { scope: :child_organisation_id, message: "You have already added this housing provider" }, on: :housing_provider
+  validates :child_organisation_id, uniqueness: { scope: :parent_organisation_id, message: "You have already added this managing agent" }, on: :managing_agent
+  validate :validate_housing_provider_owns_stock, on: :housing_provider
 
 private
 
-  def validate_housing_provider_relationship
-    if parent_organisation_id.blank?
-      errors.add :related_organisation_id, "You must choose a housing provider"
-    elsif OrganisationRelationship.exists?(child_organisation:, parent_organisation:)
-      errors.add :related_organisation_id, "You have already added this housing provider"
-    elsif parent_organisation_id.present? && !parent_organisation.holds_own_stock
-      errors.add :related_organisation_id, I18n.t("validations.scheme.owning_organisation.does_not_own_stock")
-    end
-  end
-
-  def validate_managing_agent_relationship
-    if child_organisation_id.blank?
-      errors.add :related_organisation_id, "You must choose a managing agent"
-    elsif OrganisationRelationship.exists?(child_organisation:, parent_organisation:)
-      errors.add :related_organisation_id, "You have already added this managing agent"
+  def validate_housing_provider_owns_stock
+    if parent_organisation_id.present? && !parent_organisation.holds_own_stock
+      errors.add :parent_organisation_id, I18n.t("validations.scheme.owning_organisation.does_not_own_stock")
     end
   end
 end
diff --git a/app/views/organisation_relationships/_related_organisation_select_question.html.erb b/app/views/organisation_relationships/_related_organisation_select_question.html.erb
index cc27c2b8b..551bce5ed 100644
--- a/app/views/organisation_relationships/_related_organisation_select_question.html.erb
+++ b/app/views/organisation_relationships/_related_organisation_select_question.html.erb
@@ -1,3 +1,3 @@
 <% answers = question.answer_options.map { |key, value| OpenStruct.new(id: key, name: value) } %>
-<%= f.govuk_collection_select :related_organisation_id, answers, :id, :name, label: { hidden: true }, "data-controller": "accessible-autocomplete" do %>
+<%= f.govuk_collection_select field, answers, :id, :name, label: { hidden: true }, "data-controller": "accessible-autocomplete" do %>
 <% end %>
diff --git a/app/views/organisation_relationships/add_housing_provider.html.erb b/app/views/organisation_relationships/add_housing_provider.html.erb
index 4171e89af..cb95fd6ac 100644
--- a/app/views/organisation_relationships/add_housing_provider.html.erb
+++ b/app/views/organisation_relationships/add_housing_provider.html.erb
@@ -18,6 +18,7 @@
     <% answer_options[organisation[0]] = organisation[1] %>
   <% end %>
   <%= render partial: "organisation_relationships/related_organisation_select_question", locals: {
+    field: :parent_organisation_id,
     question: Form::Question.new("", { "answer_options" => answer_options }, nil),
     f:,
   } %>
diff --git a/app/views/organisation_relationships/add_managing_agent.html.erb b/app/views/organisation_relationships/add_managing_agent.html.erb
index 5bf3ac354..173e845ad 100644
--- a/app/views/organisation_relationships/add_managing_agent.html.erb
+++ b/app/views/organisation_relationships/add_managing_agent.html.erb
@@ -18,6 +18,7 @@
     <% answer_options[organisation[0]] = organisation[1] %>
   <% end %>
   <%= render partial: "organisation_relationships/related_organisation_select_question", locals: {
+    field: :child_organisation_id,
     question: Form::Question.new("", { "answer_options" => answer_options }, nil),
     f:,
   } %>