Lloyd Blankfein, Goldman Sachs' chief executive, called Vikram Pandit, his Citigroup counterpart, last month to discuss a merger, in a dramatic example of the secret manoeuvring that preceded the government bail-out of the financial sector.

The call, which was made at the tentative suggestion of the regulatory authorities or at least with their blessing, was made shortly after Goldman had won surprise approval to convert itself from a securities firm into a commercial bank on September 21, according to several people familiar with the events.