Government finances for January showed a surplus of £4.7bn, the Office for National Statistics has said.
That was less than the £6bn surplus recorded a year ago.
For the financial year-to-date, government borrowing was £90.7bn, which was £4bn lower than at the same point a year earlier.
January usually records a surplus due to high tax receipts, but in most other months the government borrows more money than it receives.
The total pile of government debt now stands at £1.24tn, equivalent to 74.6% of the UK’s total economic output.
The ONS figures are initial estimates and are subject to revision. They exclude the effect of bank bailouts.
The £1.3bn fall in January’s surplus when comparing with a year earlier was down to higher government spending. Tax receipts from VAT and stamp duty were up slightly, but this was offset by a fall in receipts from income and corporation tax.