HSBC is in hot water in the UK and Europe after its Swiss arm was alleged to have helped clients evade millions of pounds in tax, with Belgium preparing to issuing a police warrant for the group's directors.The bank has featured in recent court cases in the US and Europe but thousands of new leaked files indicate that there has been a pattern of tax dodging behaviour for years, according to a hoard of leaked data examined by the International Consortium of Investigative Journalists and an international collaboration of news outlets including the Guardian, Le Monde and BBC's Panorama.The leaked documents were stolen in 2007 but a computer technician working for the bank, and they include the details of more than 100,000 global clients.Those leading Belgium's investigation into the affair are now mulling the issue of an international arrest warrant for the group's directors for "not giving the required information voluntarily", according to Reuters, with the bank being accusing of offering Antwerp diamond dealers and other wealthy clients ways of hiding cash and evading tax.The UK tax authorities at HMRC have had access to the data but, apart from having recovered £135m in tax from some individuals in the leaked HSBC files, have refused to act further on the evidence.Margaret Hodge, chair of the UK parliament's public accounts committee, said: "I feel frustrated, angry and depressed ... this is clearly a huge secret industry on a massive scale, which none of us knew about. It is all about helping exceedingly rich people avoid their tax."We've been pursuing it for some time, but I don't think we knew the depth of outrageous behaviour to which they had descended."Stressing that the Swiss banking industry had operated very differently i n the past, a statement from HSBC said: "We have taken significant steps over the past several years to implement reforms and exit clients who did not meet strict new HSBC standards. HSBC's Swiss private bank has reduced its client base by almost 70% since 2007."The Guardian claimed one example of misbehaviour involved a wealthy British football club director Keith Humphreys who revealed to an HSBC manager that his father's $430,000 Swiss account was "not declared" to the UK tax authorities.According to reports, Humphries claimed that one HSBC employee advised him on how to access undeclared offshore money through a credit card. He said: "The credit card is thus used to enable the Humphreys family to make withdrawals from 'cash points' when they are outside the UK."French authorities have judged that 99.8% of the individuals listed in the stolen data were most likely tax evading.HSBC Holdings declined after an investigative journalism and the BBC's Panorama revealed its private-banking unit profited from secret accounts for criminals.While moving funds to offshore accounts is legal, deliberately hiding money to dodge tax is illegal.