You've found an error or had a letter from HMRC
Two questions shape what happens next. Is the disclosure unprompted (you found it first) or prompted (HMRC asked)? Is it a single line or a systemic pattern across many entries? Unprompted, full-cooperation disclosures attract the lowest penalty loading. Work through the steps below to scope your exposure, choose the right disclosure route, and check whether valuation — the commonest underlying error — is the cause.
1. Scope your exposure
Understand when liability arises, the civil/criminal split, and how voluntary disclosure mitigates penalties
2. Choose your disclosure route
Decide between a C2001 voluntary amendment and responding to a National Clearance Hub enquiry letter
3. Check the underlying error class
Most declaration errors trace back to valuation — confirm the method used and whether adjustments were applied correctly