VCAS6550 - Cash accounting scheme: Leaving the scheme: Accounting for tax on deregistration
Regulation 63(1) requires businesses that deregister to account for VAT on supplies made and received within 2 months of deregistering. These requirements are amplified in Notice 731 Cash Accounting (GOV.UK).
63(1) Where a person operating the scheme ceases business or ceases to be registered he shall within two months or such longer period as the Commissioners may allow, make a return accounting for, and pay, VAT due on all supplies made and received up to the date of cessation which has not otherwise been accounted for, subject to any adjustment for credit for input tax.
Occasionally the final return will not be submitted and an assessment will be necessary. Guidance on how to assess can be found in VAT Assessment and Error Correction Manual (VAEC).