HSBC left itself open to criminal charges in the UK over its Swiss tax-dodging scandal, ex-director of public prosecutions Lord Ken Macdonald says.
The QC said there were strong grounds to investigate the bank for “cheating” HM Revenue and Customs (HMRC).
He added that HMRC’s decision not to prosecute was “seriously flawed”.
Allegations emerged earlier this month that the bank had helped hundreds of people evade UK tax using hidden HSBC accounts in Geneva.
Also on Sunday, Chief Secretary to the Treasury Danny Alexander told the BBC the Liberal Democrats wanted to introduce new laws on tax evasion.
He told the Andrew Marr Show the party wanted to make those who facilitate any tax evasion, for example lawyers, accountants and banks, as culpable as those who evade tax themselves.
He said the party would “seek to pursue this [in government] over the next few weeks” but, if there was not enough time before the general election, the proposal would form a key part of the party’s manifesto.
In a legal opinion prepared for consumer group SumOfUs, Lord Macdonald said: “It seems clear, from the evidence we have seen, that there exists credible evidence that HSBC Swiss and/or its employees have engaged over many years in systematic and profitable collusion in serious criminal activity against the exchequers of a number of countries.
“The corporate and wholesale nature of HSBC’s Swiss’ apparent involvement in what amounts to grave cross border crime makes it all the more obvious that the relevant evidence, once it came the attention of HMRC, should have been the subject of urgent and sustained criminal investigation.”
Despite the evidence being in the hands of HMRC for nearly five years, no action has so far been taken against the bank.
Top HMRC officials have been lambasted by MPs on the Public Accounts Committee for their “pathetic” response to the evidence.
Last week, the Financial Conduct Authority said it would look into the scandal, while the Bank of England and the Serious Fraud Office have indicated they may do the same.
HSBC published a full-page apology in several Sunday newspapers last week for the past behaviour of its private bank in Geneva, and reports suggest it could make another apology this week.
The bank publishes its full-year results on Monday morning.