VATREG39500 - Registration in respect of relevant supplies: exemption from registration
VAT Act 1994, Schedule 3A, paragraph 7(1) provides that, if a person is making mainly or wholly zero-rated relevant supplies, he can apply for exemption from registration. Any person wishing to apply for exemption must complete a VAT 1C and should enclose a letter confirming the request and explaining why his supplies are zero-rated.
As the legislation is similar to that in Schedule 1, you should refer to the guidance VATREG18000 on how to deal with applications (including retrospective applications) and what to do where a business changes its circumstances.