Yes, and it is a routine job rather than a confession. Catch-up work starts with whatever exists — bank statements, an app full of receipts, a carrier bag — and rebuilds each year in sequence, because you cannot do the recent ones without the opening position from the older ones. Where records are genuinely missing we reconstruct from bank data and reasonable estimates, and where an estimate is unavoidable we disclose it rather than presenting a guess as fact. If returns are late, the priority is usually to file rather than to perfect, because late filing penalties accrue while you polish. HMRC treats an unprompted disclosure very differently from one that follows their letter, so the time to start is before they write, not after.