HMRC had forced a number of top banks, including Barclays, HSBC, HBOS, Royal Bank of Scotland and Lloyds TSB to disgorge details of their customers' offshore accounts, and had left it to the banks to left it to the banks to tell their customers about the amnesty. But just a week before the amnesty was due to expire, alarmed by the poor take-up, HMRC sent an emergency letter to half of the targeted 400,000.

Eventually just 50,000 people took advantage of the amnesty, which capped penalties at 10% of any unpaid tax, leaving the Treasury with the onerous and costly task of pursuing the remaining 350,000, many of whom no doubt live in foreign countries.

However, McCann is warning the thousands of people who have not come forward that ultimately there is no escape. “HMRC has the names and account numbers of all 400,000 investors potentially affected. They will sift their way through the entire pile, even if it takes years, and they will certainly go after the people they believe haven’t made a disclosure,” he said. “If you need to make such a disclosure, you should do so as soon as possible. The situation will not be as good as the amnesty, but it will be better than sticking your head in the sand and being held to account several months, or even years down the line."

“From the public’s point of view, this is a costly fiasco," continues McCann. "HMRC will have to divert enormous resources into resolving this huge issue. There could be thousands of tax investigations and hundreds of prosecutions – all paid for by the tax payer.”

McCann says that many account-holders may have been daunted by the sheer size of settlement amounts. “Any disclosure must include details of the interest paid on funds held offshore, as well as consideration with regard to information on where the funds came from in the first place. Where an incomplete disclosure is made the taxpayer may be open to prosecution,” he added. “Disclosures must covers all types of UK taxes, potentially going back 20 years. Full interest will be charged on unpaid tax. Anyone with any concerns about the case should contact a professional adviser.”

People who, in HMRC’s opinion, owe in excess of GBP500,000 of unpaid tax will be dealt with by the national “Special Civil Investigations” team. The majority will be dealt with under HMRC’s “Civil Investigation of Fraud” (CIF) procedure. Those who HMRC believe owe between GBP75,000 and GBP500,000 in undisclosed tax will receive the attentions of HMRC’s Civil Investigation of Fraud teams, again using CIF procedure. Those who HMRC believes have undisclosed tax of less than GBP75,000 will be dealt with by their local tax offices, which will raise enquiries into their previous tax returns.