Another 2.7% is the cyclical deficit, which should disappear of its own accord as the economy recovers boosting tax revenues and reducing unemployment benefit payments.

BBC: The Budget in numbers

One assumes that at some point things get back to normal and revenues begin to rise and the cyclical part of the deficit goes away.

FORBES: The Path To Profligacy

"We're in a much worse situation than in 1992 because more of this deficit is structural rather than cyclical and the entitlement explosion is closer at hand, " says Goldman Sachs chief economist William Dudley.

FORBES: Your Next Tax Hike

"The deficit will be reduced by the cyclical expansion that is now under way, which will absorb spare capacity in the economy, " Charles Collyns, deputy director of the IMF's Western Hemisphere Department, told reporters.

CNN: IMF: U.S. needs to balance budget

In economic terms, if the economy were still growing very slowly, and the deficit was both small and purely cyclical, that might not be an economic catastrophe: but it would be massively embarrassing politically, largely because of the White House's attempts to cover up the disappearance of the surplus.

ECONOMIST: That elusive surplus | The

And if a bigger deficit than expected does open up for cyclical reasons, Mr Brown would be unlikely to need to try and close it.

ECONOMIST: Gordon Brown and the Bank