diff --git a/Gemfile b/Gemfile
index 14c50289e..9bc8d4487 100644
--- a/Gemfile
+++ b/Gemfile
@@ -82,6 +82,7 @@ gem "simple_form", "~> 5.0"
 gem "country_select", "~> 3.1"
 gem "email_validator"
 gem "enumerize"
+gem "phonelib"
 
 # PDF generation
 gem "prawn"
diff --git a/Gemfile.lock b/Gemfile.lock
index 8d1711265..c352991ed 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -400,6 +400,7 @@ GEM
     pg_search (2.3.6)
       activerecord (>= 5.2)
       activesupport (>= 5.2)
+    phonelib (0.9.2)
     poltergeist (1.18.1)
       capybara (>= 2.1, < 4)
       cliver (~> 0.3.1)
@@ -777,6 +778,7 @@ DEPENDENCIES
   pdf-inspector
   pg
   pg_search (~> 2.3.3)
+  phonelib
   poltergeist
   prawn
   prawn-table
diff --git a/app/models/user.rb b/app/models/user.rb
index 2e946b64d..f6520a219 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -25,17 +25,8 @@ class User < ApplicationRecord
   validates :phone_number, presence: true, if: -> { first_step? }
   validates :password, confirmation: true
 
-  validates :phone_number, length: {
-    minimum: 7,
-    maximum: 20,
-    message: "This is not a valid telephone number",
-  }, if: -> { first_step? }
-
-  validates :company_phone_number, length: {
-    minimum: 7,
-    maximum: 20,
-    message: "This is not a valid telephone number",
-  }, allow_blank: true, if: -> { second_step? }
+  validates :phone_number, phone: true, if: -> { first_step? }
+  validates :company_phone_number, phone: { allow_blank: true }, if: -> { second_step? }
 
   validates_with AdvancedEmailValidator
 
diff --git a/config/initializers/phonelib.rb b/config/initializers/phonelib.rb
new file mode 100644
index 000000000..4802c4220
--- /dev/null
+++ b/config/initializers/phonelib.rb
@@ -0,0 +1 @@
+Phonelib.default_country = "GB"
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 611696925..6a14fd886 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -79,6 +79,10 @@ en:
       models:
         user:
           attributes:
+            phone_number:
+              invalid: Enter a phone number, like 01635 960 001, 07701 900 982 or +44 808 157 0192
+            company_phone_number:
+              invalid: Enter a phone number, like 01635 960 001, 07701 900 982 or +44 808 157 0192
             email:
               invalid: 'Email is invalid - enter a valid email address'
             role:
diff --git a/spec/factories/user_factory.rb b/spec/factories/user_factory.rb
index 03c931f7c..259c6b0a8 100644
--- a/spec/factories/user_factory.rb
+++ b/spec/factories/user_factory.rb
@@ -6,7 +6,7 @@
     email
     role { "regular" }
     agreed_with_privacy_policy { "1" }
-    sequence(:phone_number) { |n| "1111111#{n}" }
+    sequence(:phone_number) { |n| "020 4551 008#{n.to_s[-1]}" }
     confirmed_at { Time.zone.now }
 
     trait :completed_profile do
@@ -18,7 +18,7 @@
       company_city { "London" }
       company_country { "GB" }
       company_postcode { "SE16 3SA" }
-      sequence(:company_phone_number) { |n| "7777777#{n}" }
+      sequence(:company_phone_number) { |n| "020 4551 008#{n.to_s[-1]}" }
       prefered_method_of_contact { "phone" }
       qae_info_source { "govuk" }
       role { "regular" }
diff --git a/spec/features/users/account_creation_spec.rb b/spec/features/users/account_creation_spec.rb
index 48db13a3c..52e62eda0 100644
--- a/spec/features/users/account_creation_spec.rb
+++ b/spec/features/users/account_creation_spec.rb
@@ -32,27 +32,30 @@
   end
 
   context "Account details fulfillment" do
+    def fill_in_and_submit_account_details_form
+      fill_in("Title", with: "Mr")
+      fill_in("First name", with: "FirstName")
+      fill_in("Last name", with: "LastName")
+      fill_in("Your job title", with: "job title")
+      fill_in("Your telephone number", with: phone_number)
+
+      click_button("Save and continue")
+    end
+
     context "regular user" do
       let!(:user) { create(:user, role: "regular") }
 
       before do
         create(:settings, :submission_deadlines)
         login_as(user, scope: :user)
+        visit root_path
+        fill_in_and_submit_account_details_form
       end
 
-      let(:phone_number) { "1231233214354235" }
+      let(:phone_number) { "020 4551 0081" }
       let(:company_name) { "BitZestyOrg" }
 
       it "adds the Account details" do
-        visit root_path
-        fill_in("Title", with: "Mr")
-        fill_in("First name", with: "FirstName")
-        fill_in("Last name", with: "LastName")
-        fill_in("Your job title", with: "job title")
-        fill_in("Your telephone number", with: phone_number)
-
-        click_button("Save and continue")
-
         expect(page).to have_content("Contact preferences")
         click_button("Save and continue")
 
@@ -63,6 +66,16 @@
         expect(user.phone_number).to eq(phone_number)
         expect(user.completed_registration?).to eq(true)
       end
+
+      context "with an invalid phone number" do
+        let(:phone_number) { "020 4551 008" }
+
+        it "displays an error message" do
+          expect(page).to have_content(
+            I18n.t("activerecord.errors.models.user.attributes.phone_number.invalid"),
+          )
+        end
+      end
     end
 
     context "admin user" do
@@ -71,27 +84,20 @@
       before do
         create(:settings, :submission_deadlines)
         login_as(user, scope: :user)
+        visit root_path
+        fill_in_and_submit_account_details_form
       end
 
-      let(:phone_number) { "1231233214354235" }
+      let(:phone_number) { "020 4551 0081" }
       let(:company_name) { "BitZestyOrg" }
 
       it "adds the Account details" do
-        visit root_path
-        fill_in("Title", with: "Mr")
-        fill_in("First name", with: "FirstName")
-        fill_in("Last name", with: "LastName")
-        fill_in("Your job title", with: "job title")
-        fill_in("Your telephone number", with: phone_number)
-
-        click_button("Save and continue")
-
         expect(page).to have_content("Contact preferences")
         click_button("Save and continue")
 
         expect(page).to have_content("Organisation details")
         fill_in("Name of the organisation", with: company_name)
-        fill_in("The organisation's main telephone number", with: "9876544")
+        fill_in("The organisation's main telephone number", with: "020 4551 0082")
 
         click_button("Save and continue")
 
@@ -102,6 +108,16 @@
         expect(user.phone_number).to eq(phone_number)
         expect(user.company_name).to eq(company_name)
       end
+
+      context "with an invalid phone number" do
+        let(:phone_number) { "020 4551 008" }
+
+        it "displays an error message" do
+          expect(page).to have_content(
+            I18n.t("activerecord.errors.models.user.attributes.phone_number.invalid"),
+          )
+        end
+      end
     end
   end
 end
diff --git a/spec/features/users/collaborator_registration_flow_spec.rb b/spec/features/users/collaborator_registration_flow_spec.rb
index dfff61278..a0aba90b4 100644
--- a/spec/features/users/collaborator_registration_flow_spec.rb
+++ b/spec/features/users/collaborator_registration_flow_spec.rb
@@ -8,9 +8,6 @@
 
   before do
     create(:settings, :submission_deadlines)
-  end
-
-  it "creates and account and collaborator is able to collaborate" do
     login_as(acc_admin, scope: :user)
 
     visit new_account_collaborator_path
@@ -19,7 +16,7 @@
     fill_in("First name", with: "First Name")
     fill_in("Last name", with: "Last Name")
     fill_in("Job title", with: "job title")
-    fill_in("Telephone number", with: "1231233214354235")
+    fill_in("Telephone number", with: "020 4551 0081")
     fill_in("Email", with: "collab@example.com")
     first("input#collaborator_role_account_admin").set(true)
 
@@ -35,12 +32,14 @@
     visit root_path
 
     click_button("Save and continue")
+  end
 
+  it "creates and account and collaborator is able to collaborate" do
     expect(page).to have_content("Contact preferences")
     click_button("Save and continue")
 
     fill_in "Name of the organisation", with: "Disney"
-    fill_in "The organisation's main telephone number", with: "012312312"
+    fill_in "The organisation's main telephone number", with: "020 4551 0082"
     click_button("Save and continue")
 
     # collaborator page
@@ -48,4 +47,19 @@
 
     expect(page).to have_content("Applying for a King's Award for your organisation")
   end
+
+  context "when the company_phone_number is invalid" do
+    it "displays an error message" do
+      expect(page).to have_content("Contact preferences")
+      click_button("Save and continue")
+
+      fill_in "Name of the organisation", with: "Disney"
+      fill_in "The organisation's main telephone number", with: "020 4551 008"
+      click_button("Save and continue")
+
+      expect(page).to have_content(
+        I18n.t("activerecord.errors.models.user.attributes.company_phone_number.invalid"),
+      )
+    end
+  end
 end