HM Revenue & Customs
Wealthy Britons with accounts in Liechtenstein have been targeted in a global tax-evasion investigation.
HM Revenue & Customs hopes to recover £300m from those who have deposited more than £1bn in the Alpine tax haven.
Some of the 300 under investigation may settle out of court. Germany, the US and other countries have launched a similar crackdown.
The investigation is based on data obtained from a paid informant who once worked for Liechtenstein's LGT Bank and who sold information to Germany and other tax authorities.
The Organisation for Economic Co-operation and Development (OECD) lists Liechtenstein as one of only three states remaining on its blacklist of "unco-operative tax havens."
HMRC is also launching a wider investigation into offshore accounts. Spokesman Paul Franklin said those found to have evaded taxes must pay the amount they owe plus interest and a penalty of up to 100% of the unpaid tax.
"We're dealing with very wealthy people who have used Liechtenstein's secrecy laws to escape UK tax regulations" he said. In certain circumstances, those found guilty of tax evasion can face a prison sentence of up seven years.
The investigation is expected to be completed within three years.
Maurice Martin from law firm Irwin Mitchell said: "HMRC's investigation into the affairs of those banking in tax haven Liechtenstein is wholly in line with its policy over a number of years. The fact that HMRC has been prepared to pay an ex-employee from LGT Bank for the identity of account holders is telling of the lengths to which it is prepared to go to crack down on tax evasion. The individual in question, Heinrich Kieber, is currently subject to an international arrest warrant.
"HMRC's reference to possible prosecution for tax evasion is not illusory. Undeclared income owed by UK residents arising from offshore bank accounts has always been regarded as a very serious matter under HMRC's internal policy and guidelines.
"Irwin Mitchell has partners who specialise in this area and who each have over 30 years experience in the field."