Every VAT-registered business, without exception for size. This is the point most people get wrong, because MTD for VAT arrived in stages: it applied to businesses above the registration threshold from April 2019, and was extended to all VAT-registered businesses — including voluntarily registered ones below the threshold — from April 2022. So if you are registered for VAT, you are in MTD for VAT now, regardless of turnover. It has nothing to do with the April 2026 Income Tax dates, which are a separate regime with separate thresholds. If you are voluntarily registered, turning over £40,000 and still keying your return into HMRC’s website, you have been non-compliant for some years and should fix it rather than wait for someone to notice.