In spite of another round of reassurance from the heads of Europe’s biggest investment banks this month, doubts still persist about a business model that until now relied on cheap debt and inflated balance sheets.

UBS, Deutsche Bank and Credit Suisse rounded off their worst years by announcing bruising fourth-quarter losses, battered by a combination of writedowns, trading losses and bad debts. At the heart were the investment banking units, the source of more than one third of pre-tax profit at UBS and Credit Suisse in the heyday of 2006 and almost two thirds at Deutsche Bank.