VAEC9580 | Demand for VAT: Assessment is not appropriate: Issue of an invoice for non supplies
From HM Revenue & Customs · VAT Assessments and Error Correction
Where a tax invoice is issued for non-supplies, for instance where there has been a transfer of a going concern, and tax is charged but not accounted for, you cannot issue the supplier with a VAT 655 assessment for the tax charged in error.
There is no liability to account for tax on non-supplies. You should take corrective action against either:
the recipient of the non-supplies by disallowing any claim to input tax deduction. An assessment should be made on form VAT655. Interest should not be inhibited, but there may be a need to inhibit MP or,
the supplier under VATA94 Schedule 11 paragraph 5, see VAEC9600.
The action you take should depend on which course is likely to be the most economical and successful.