At some point this autumn, some poor Treasury official had the difficult job of telling Gordon Brown that the government’s piggy bank had sprung a £5bn leak. Taxes would have to go up, the government would have to borrow more and net public investment plans would be cut. It cannot have been an easy meeting.

The news would have been an unwelcome surprise. With the economy growing faster than forecast in 2006, tax revenues on target and faster long-run growth rates in prospect, the chancellor would have been expecting to deliver a triumphant last pre-Budget report with tax cuts, lower borrowing and higher investment. He may have been hoping to deliver all three, propelling him seamlessly to Number 10.