The boss of HSBC said the bank had sometimes failed to live up to the standards expected of it, in his first response to allegations of helping hundreds of people dodge taxes.
HSBC this week admitted failings in compliance and controls in its Swiss private bank after media allegations it may have enabled clients to avoid paying tax.
However CEO Stuart Gulliver said many people alleged to have been clients had long since left and some never were clients.
The disclosures have sparked a political row in Britain over practices at HSBC, Europe's biggest bank, and whether tax authorities had done enough to pursue possible wrongdoers.
Mr Gulliver said in a memo to staff seen by Reuters he had been called to give evidence to lawmakers over the allegations.
HSBC Chairman Douglas Flint has already been called to answer questions about the issue on 25 February.
"I share your frustration that the media focus on historical events makes it harder for people to see the efforts we have made to put things right," Mr Gulliver said in the memo.
"But we must acknowledge we sometimes failed to live up to the standards the societies we serve rightly expected from us."
The International Consortium of Investigative Journalists, which coordinated the release of details of leaked data about HSBC clients up to 2007, said the list of people who held accounts with the Swiss arm included royalty, sports and rock stars, Hollywood actors, politicians and arms dealers.
Having a Swiss bank account is not illegal and many are held for legitimate purposes.
The Guardian newspaper said HSBC had provided accounts for clients implicated in African corruption scandals, blood diamond trading and others alleged to have been involved in bribery and cocaine smuggling.
Mr Gulliver said of about 140 names mentioned in media reports, 106 were no longer clients. Several left the bank before the data was taken. And a number of other named individuals had never been clients.
Mr Gulliver said HSBC's Swiss bank had been completely overhauled since 2008 and HSBC was now run with far greater central control and with more than 7,000 compliance staff, double the number in 2011.
He said he and Mr Flint welcomed the opportunity to explain the changes to Britain's Treasury Committee.
One of the lawmakers on the parliamentary panel said it could also quiz former HSBC Chairman Stephen Green, who held the post from 2006 to 2010 and was Britain’s trade minister from 2011 until 2013.