VATAFRS0270 | Operation of the scheme: records to be kept by the farmer
From HM Revenue & Customs · VAT Agricultural Flat Rate Scheme
The farmer must keep all normal business records and copies of all invoices on which the flat rate addition is shown for a period of 6 years.
Note for managers: You have the discretion to agree a shorter period for the retention of records if a farmer requests it. Follow the general guidance in VATREC when considering such requests.