You need enough to prepare a correct return and to prove the figures if HMRC asks: all sales and other income, all business expenses, bank and cash records, and — if you are VAT registered — a VAT account. If you hold stock, you need year-end stock figures. If you own business assets, you need records of what you bought, when, and for how much. The test HMRC applies is whether the records support the return, so a bank statement alone is rarely enough: it shows £340 left your account but not what it was for or whether it was allowable. That is why the receipt matters as much as the payment. Under MTD these same records simply have to be kept digitally rather than in a folder.