Clarify who uses Stripe (not everyone)

source/using-govuk-pay.html.erb

@@ -45,7 +45,7 @@ title: Using GOV.UK Pay
 
         <h3 class="govuk-heading-s">Payment Service Provider</h3>
         <p class="govuk-body">
-          You need a Payment Service Provider (PSP) to process payments through GOV.UK&nbsp;Pay. We’ve already procured Stripe as our payment provider for you.
+          You need a Payment Service Provider (PSP) to process payments through GOV.UK&nbsp;Pay. We’ve already procured Stripe as our payment provider for you if you work for a local authority, police force or a government-owned charitable group.
         </p>
         <p class="govuk-body">
           Alternatively, if you are a central government or health sector organisation, you can use Government Banking’s centralised contract currently held with Worldpay.