Update Jan 2, 2024: You need to contact HMRC to request a paper VAT1 form and return it with the VAT1A form.
To register for VAT for distance selling into Northern Ireland, use form VAT1A and also complete a paper VAT1 form. Send the completed application form to BT VAT, HM Revenue and Customs, BX9 1WR. For more information on when to register for UK VAT and how to register, refer to the related forms and guidance provided.
Source gov.uk
