When the US authorities allowed Lehman Brothers to fail last month, nobody expected that the decision would trigger a wave of nationalisations, rescues and government interventions across Europe.

Yet the shockwaves caused by the bankruptcy of the Wall Street investment bank was this week responsible for toppling financial institutions in Iceland, Belgium, Britain and Germany; causing investors and customers to question the stability of even the soundest lender; and forcing European governments to take unprecedented steps to shore up confidence in their banks.