Legally yes if you are a sole trader or landlord, but it is the single most expensive habit we see. Nothing prohibits it — you and the business are the same legal person — but every transaction then has to be sorted by hand rather than flowing in through a bank feed, which is precisely the manual work MTD is designed to remove. It also weakens you under enquiry, because HMRC can ask to see the whole account and you lose the clean line between business and private spending. For a limited company it is different and more serious: the company’s money is not yours, and paying personal costs from the company account creates director’s loan and benefit-in-kind problems. A separate account costs little and pays for itself immediately.