The government borrowed more than expected in February, figures released just days ahead of the UK Budget show.
Public sector net borrowing - the government's preferred measure - hit £2.3bn in February, up from £1.4bn the Office for National Statistics said.
As a result, over the first 11 months of the fiscal year the total UK deficit stood at £31.7bn, compared with the Gordon Brown's forecast of £37bn.
Many experts have warned Mr Brown will have to raise taxes to cut borrowing.
In December the International Monetary Fund (IMF) warned that Mr Brown's tax forecasts had been too optimistic , adding he may have to increase taxes by £6bn in order to meet his forecasts.
'Disappointing' figures
The latest deficit figures were the worst recorded for February since the government came to power in 1997.
"The figures are disappointing on both the accruals and the cash measures and the story this month is that there has been an acceleration in expenditure and a slowdown in tax receipts growth," Investec analyst Philip Shaw said.
The deterioration in the figures came as government spending rose by 8.4% in February compared to a year earlier to £40.4bn, more than offsetting a 5.6% rise in total receipts to £31.2bn.
Mr Brown has predicted that he will meet his "golden rule" that current borrowing and spending should balance over the economic cycle.
However, even if he meets his target in the current cycle - which is due to end in 2008 - analysts have warned taxes will have to rise, or spending be cut, by around £10bn over the next few years to balance the books.
Despite the warnings, most commentators have predicted few changes in Mr Brown's upcoming budget as he paves the way to succeed current prime minister Tony Blair.
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