More than 50 Canadian clients of UBS have come forward to disclose unpaid taxes, and investigations so far have found C$7 million ($6.4 million) in unreported income, Canada's tax authority said, according to Reuters.

The voluntary disclosures follow in the wake of UBS’s tax case in the US, in which it has paid a $780 million sum to settle criminal charges that it helped wealthy US citizens evade taxes. The Swiss and US governments have also reached an agreement under which UBS will pass over details on up to 4,450 client accounts.

The move has been seen as a historic breach of Switzerland’s centuries-old tradition of bank secrecy.

"Twenty of the voluntary disclosures that we've received have now been finalized ... and the completed cases - those 20 - involve about C$7 million in unreported income. And we do expect to receive more in the future," a Revenue Canada spokesperson told the news agency.

Revenue Canada, keen to clamp down on tax evasion by offshore account holders, has met with UBS lawyers to try to compel the bank to reveal its Canadian account holders who may have failed to report income.

Revenue Canada said about 56 voluntary disclosures have been made in total, with 20 completed and dozens more still undergoing review.