(Reuters) -- HSBC Holdings PLC published full-page advertisements in British newspapers Sunday featuring in a letter its “sincerest apologies” for past practices at its Swiss private bank, which has been accused of helping clients to evade tax. Europe’s biggest bank admitted failings in compliance and controls in its Swiss operation after media reports that said it had helped wealthy customers to conceal millions of dollars of assets up to 2007.

Britain’s Treasury Committee has called the bank’s chairman and CEO to give evidence on the matter Feb. 25, according to a memo seen by Reuters Friday.

The bank’s letter published in a number of newspapers Sunday was signed by CEO Stuart Gulliver and said that the reports had been a “painful experience” for its customers, shareholders and employees.

“We must show we understand that the societies we serve expect more from us,” Gulliver wrote. “We therefore offer our sincerest apologies.”

The bank said the vast majority of the 140 people named in reports as customers of its Swiss bank had left and that it has since established much tighter controls on who it accepts as customers.

“We have absolutely no appetite to do business with clients who are evading their taxes or who fail to meet our financial crime compliance standards,” he said.

The fallout from the claims caused the bank’s former boss Stephen Green to step down Saturday at financial-services lobby group TheCityUK.

(Reporting by Paul Sandle; Editing by David Goodman)