HSBC, Europe's biggest bank, said on Friday it was investigating the alleged loss of data for clients in Jersey but had not been notified of any investigation by tax authorities.
The Daily Telegraph has reported that British tax authorities were examining details of more than 4,000 UK clients of HSBC in Jersey after a whistle-blower handed them a list of names, addresses and account balances.
HM Revenue & Customs (HMRC) said in a statement: "We can confirm we have received the data and we are studying it. We receive information from a very wide range of sources which we use to ensure the tax rules are being respected."
HSBC said it was investigating the alleged loss of client data "as a matter of urgency."
"We have not been notified of any investigation in relation to this matter by HMRC or any other authority but, should we receive notification, we will cooperate fully with the authorities," the bank said in a statement.
This could mark another potential blow for HSBC which has been slammed by U.S. regulators for lax anti-money laundering controls in Mexico and elsewhere, and last year saw thousands of its Swiss clients probed by the UK taxman.
The bank's London-listed shares dipped 0.2 percent by 4 a.m EDT, in line with a weak European banking index.
The Daily Telegraph report said Britain's revenue service was combing through the list it had been given of HSBC's Jersey clients to establish whether some used the offshore bank accounts to avoid paying UK taxes.
The list identifies 4,388 British-based people holding 699 million pounds ($1.1 billion) in current accounts and includes celebrities, bankers, doctors, mining and oil executives and oil workers, it the Telegraph wrote. The list also includes about 4,000 account holders with addresses outside Britain.
HSBC said earlier this week that a U.S. probe into anti-money laundering failures could result in a fine well over $1.5 billion and lead to criminal charges as well.
Tax authorities around the world are stepping up their efforts to uncover the identities of those who avoid taxes by hiding money in offshore accounts.
HSBC said on Friday it was "fully committed to adoption of the highest global standards including the procedures for the acceptance of clients."
(Reporting by Natalie Huet and Steve Slater; Editing by Will Waterman and Jane Merriman)