The UK's tax authority has confirmed that it has paid an informant for data regarding British citizens who have accounts in tax haven Liechtenstein.
The UK says it is trying to protect the UK exchequer
HM Revenue and Customs (HMRC) confirmed the move after a Sunday Times report, but would not say how much it had paid the informant.
HMRC said it was seeking "to protect the UK exchequer from those who seek to hide behind secrecy laws".
Separately Germany is involved in its own probe over Liechtenstein accounts.
The Sunday Times newspaper claimed the amount paid to the informant was £100,000 - but that figure was not confirmed.
HMRC said it had made the move in a bid to protect the UK against those trying to "deprive the UK of tax revenues to which it is entitled".
Meanwhile, Germany has launched a probe into tax evasion using data also from an anonymous informant, who was reportedly paid 5m euros (£3.7m; $7.4m).
In response, the country's head - Prince Alois von und zu Liechtenstein - has argued that Germany's move is illegal.
Liechtenstein is now conducting its own investigation on the subject.
The Organisation for Economic Cooperation and Development lists Liechtenstein as one of only three states remaining on its blacklist of "uncooperative tax havens".