British bank HSBC has taken out full-page adverts in several national UK newspapers offering "sincerest apologies" for the standards in place at its Swiss operations eight years ago.

In the open letter to its customers, shareholders and colleagues, the bank's group chief executive Stuart Gulliver described recent media coverage about past practices at the Swiss Private Bank as a "painful experience".

Revenue confirmed last week it recouped €4.5m in unpaid taxes after the massive leak of data on offshore account holders.

The money related to 20 Irish account holders, whose information arose in a batch of 60,000 files about HSBC clients.

Three successful prosecutions have also been completed as a result of the information which Revenue received in 2010.

The secret files relate to the Swiss operation of the bank between 2005 and 2007 - and appear to show that in some cases, HSBC helped clients avoid paying tax.

The documents have led to criminal investigations in several countries and attempts to get the money back after being stolen by an IT worker in 2007 and passed to authorities in France.

The accounts hold nearly stg£78bn (€9.42bn) of assets.

The advert by the bank states: "We would like to provide some reassurance and state some of the facts that lie behind the stories."

"The media focus has been on historical events that show the standards to which we operate today were not universally in place in our Swiss operations eight years ago."

"We must show we understand that the societies we serve expect more from us. We therefore offer our sincerest apologies."

The bank added that since 2008 it had established a "much tighter central control around who are our customers".

It said it had also implemented tougher standards around tax transparency.

Earlier this week, Mr Gulliver sent a memo to the bank's staff saying the revelations were painful and frustrating.

The adverts come amid a political row over tax avoidance, with UK Labour leader Ed Miliband on Saturday vowing to carry out an inquiry into the UK's tax authority should his party win power in the next general election there.