It is not a formal investigation, and the next 12 – 18 months will be incredibly stressful. HMRC has asked you to file a disclosure within 60 days or deny that you have committed any tax evasion or tax fraud. You would need an accountant to calculate the amount of tax you owe in actuality to HMRC. You must give estimated figures and write down how this happened in the disclosure. You are the best judge to estimate the income you have failed to disclose over several years. An accountant can calculate tax and consider other factors. Accountants who do not have experience in such investigations will fail to recognise untaxed income and may rely on the documents already submitted to HMRC by previous accountants. We would advise you to talk to specialist accountants and see if they can identify the untaxed income by going through documents and interviewing you about your business and events. On the other hand, a lawyer can only advise you on the law; he would still need an accountant to analyse income and calculate tax.