The argument that Northern Rock’s Granite funding programme would suck good mortgages out of the nationalised bank – put forward by the Conservatives – was roundly dismissed on Wednesday by City experts. The programme has securitised, or turned into bonds, more than £45bn ($87bn) worth of mortgages sold by Northern Rock in recent years but has no claim on assets still with the bank.

The Granite trust would need to to be fed with more mortgages in order to keep it going, but that was entirely at the discretion of the bank’s management, analysts said.