The damaging information contained in the Treasury document will cause huge embarrassment for Gordon Brown, but perhaps more worrying will be the fear that the leak is an omen that the Government has lost the confidence of its own civil servants.
In the past, leaks have been a hallmark of a government on the way out. Margaret Thatcher was hit with a leak about new rules for state aid for scientific research in 1988, but the unpopularity of John Major's government pushed leaks to record levels. A stream of documents revealed his government's U-turn on consumer protection plans and the future of a shipyard, a memo on the use of EU funds, proposed cuts to the welfare state, and details of rejected childcare reforms. Things deteriorated so badly for Mr Major that in 1996, the entire Budget was leaked to the Daily Mirror. The paper decided to hand back the document.
Worryingly for Mr Brown, the Treasury material is not the first high-profile documentation to end up in the hands of the Opposition. An internal inquiry had to be launched last year after a series of leaks from the Home Office, among them an email revealing that thousands of illegal immigrants had been cleared to work as security guards. A junior Home Office official, Chris Galley, and Tory frontbencher Damian Green were arrested over the leak, though all charges were later dropped.
Tory sources refused to say if they had held back any details with which to further embarrass the Government. But with a worker inside the Treasury now willing to help the Conservatives, more uncomfortable news may be on the way for Mr Brown.