VATREG03100 | Registration - general: how notification must be made
From HM Revenue & Customs · VAT Registration
A person who is required to be registered for VAT must notify HMRC of that liability within the statutory time limit.
Notification must be made
on the prescribed form published in VAT Notice 700/1 as required by the VAT Regulations 1995, regulation 5(1), or
electronically via HMRC's online VAT Registration Service (regulation 4A).
The forms are the VAT 1, 1A, 1B and 1C.
If the entity registering is a partnership, the partners must also complete a VAT 2 (or equivalent).