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In any case, while January’s figures were certainly a relief for Mr Brown, they were substantially flattered by one-off timing changes to oil companies’ tax payments, from a quarterly basis to three times a year. This will not be repeated. So the true health of the public finances remains in doubt — even with that £2 billion a year more from the North Sea.

In assessing the state of the Chancellor’s books, his repeated manipulations of the golden rule, meanwhile, have turned this into a red herring. The present economic cycle over which the rule is judged is now stretched over what many economists regard as a an implausibly long 12 years. A better way of judging the health of the Government’s finances is simply to look at the hefty scale of total borrowing, running at more than 3 per cent of GDP, and its sharp deterioration relative to the Chancellor’s earlier plans.

Mr Brown now expects borrowing to fall back, but this prediction is vulnerable on several fronts.

It may yet prove weaker than the Chancellor anticipates. Much of this danger emanates from abroad. In the United States, the Federal Reserve is continuing to raise interest rates, even with the full impact of its earlier tightening yet to be seen. In the eurozone, the European Central Bank is increasing rates in a way that could choke off the nascent recovery there; and in Japan, the central bank has ended its five-year long policy of flooding the Japanese financial system with liquidity.

Globally, the end of an era of very easy money could spell weaker conditions ahead, with big repercussions for the United Kingdom.

All of this implies that Mr Brown may still need to find extra revenues, raising doubts about the chances of a truly “boring” Budget. But these doubts become all the greater when you factor in the question of the Chancellor’s future spending plans — ones that will determine the shape and fortunes of a likely Brown administration.

The first outline of these will not emerge until this summer’s fundamental spending review, and the details will not be spelled out until next summer.

For now, two things are apparent. First, the success of the “Gershon” public sector efficiency drive remains doubtful, and certainly very hard to gauge, as the National Audit Office has made clear.

Second, while the Treasury has been keen enough to encourage speculation about the “eye-wateringly tight” real spending growth of 1.9 per cent a year from 2008 to 2011 pencilled into its plans, it has always has made crystal clear that these figures are far from final.

Given Mr Brown’s inevitable determination to win a convincing first election victory as prime minister, it is pretty hard to believe that this painful corset will hold.

His own past history, and basic political strategy, suggest that the Chancellor will want to ensure that he has the funds available for populist, pre-election spending in a few years’ time. And that means starting to build a war chest now. A boring Budget? Don’t bet on it.

Explore Economics

• Pre-Budget Report 2009

• Budget 2009

• World Economic Forum

• The Times MPC

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