When the then Chancellor of the Exchequer, Norman Lamont, stood outside the UK Treasury on September 16 1992 to announce that the pound had been forced out of the European exchange rate mechanism, he destroyed the Conservative party's reputation for economic competence – a political catastrophe from which it has never recovered.

On Tuesday, just over 15 years later, the Labour chancellor Alistair Darling had what may yet come to be seen as his very own ERM moment, with the same long-term impact for his government's reputation.