Luqman Arnold, the rebel UBS shareholder, has rounded on Marco Suter, the Swiss bank's chief financial officer, as part of his campaign for a boardroom shake-up and a break-up of Switzerland's biggest bank.

Mr Arnold has expressed concern that the man previously responsible for risk controls as UBS embarked on its catastrophic bet on US mortage-backed securities, was now in charge of the bank's finances.

He said: “This is not the way to ensure a radical review and correction of mistakes that led to the largest trading losses in European banking history.”

UBS shares rose 3.8 per cent yesterday as Mr Arnold, a former chief executive of UBS, whose Olivant investment vehicle has a 0.7 per cent stake in the bank, began to rally Swiss shareholders to his cause. Mr Arnold called on UBS to reverse its decision to promote Peter Kurer, the inhouse lawyer, to succeed Marcel Ospel, the ousted chairman. He said the appointment perpetuates UBS's ineffective corporate governance and insular culture.

Mr Arnold, best known for his failed bid for Northern Rock, set out his concerns in a letter to Sergio Marchionne, the UBS vice-chairman, saying UBS had destroyed SwFr90 billion (£45 billion) of shareholder value.

He added that Mr Ospel, who ousted him seven years ago, was responsible for “visiting disaster” on the bank. “UBS's reputation has been comprehensively destroyed by proprietary trading activities totally divorced from any client business,” he said.

UBS this week warned shareholders that losses on US sub-prime and related structured credit had reached $37 billion (£18.5 billion) and announced plans for an emergency $15 billion capital-raising to shore up its balance sheet.

He called on Mr Marchionne to become temporary non-executive chairman and to begin a search for an outstanding Swiss external candidate. He added that UBS should begin a programme of asset sales including the fund management arm and its Brazilian and Australasian subsidiaries.

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