Britain’s public finances showed a higher than expected monthly deficit of £14.3bn last month, official figures revealed, amid growing fears the Iran conflict could blow the government’s plans off course.

The figures from the Office for National Statistics (ONS) showed public sector net borrowing – the difference between spending and income – had widened £2.2bn year on year in February and was higher than the £8.5bn City economists had forecast.

The ONS said the data had been affected by the timing of government debt repayments, with some falling into February instead of January.

At the same time, it revised up its estimate of January’s surplus – already a record for that month – to £31.9bn, from £30.4bn previously, helped by an increase in tax payments boosting the government’s receipts.

The chancellor, Rachel Reeves, has deliberately increased borrowing for investment projects since Labour came to power in 2024 but has also raised taxes significantly, in an effort to reduce the current deficit, which measures borrowing to pay for day-to-day spending.

The latest data showed progress on that measure, with the current budget deficit in the 11 months to February down by 21.1% from the same period last year, at £62.1bn.

Total borrowing for the same period, of £125.9bn, looked on course to undershoot the Office for Budget Responsibility’s estimate for the year as a whole, of £138.3bn.

However, it came as analysts increasingly fret that higher energy prices, inflation and interest rates as a result of the Middle East conflict could jeopardise the £23bn headroom the chancellor left against her fiscal rules in last autumn’s budget.

“That the deficit numbers are broadly on track will be a welcome development for a government keen to preserve fiscal credibility at a time of unwelcome geopolitical and economic turbulence,” said Martin Beck, the chief economist at WPI Strategy. “But that turbulence means the recent fiscal numbers may prove a poor guide to what comes next.”

Nabil Taleb, an economist at consultancy PwC, said: “Interest rate cuts are inevitably deferred, inflation now looks set to pick up again, and growth remains subdued.

“That combination risks putting renewed pressure on borrowing and leaves the public finances exposed, underlining just how quickly the fiscal picture can shift.”

The government has repeatedly insisted its tax increases and measures to control inflation, including cutting energy bills from April, have put the economy in a stronger position to withstand whatever is to come.

The chief secretary to the Treasury, James Murray, said: “We have the right economic plan. Because of the choices we made before the conflict in the Middle East began, we are better prepared for a more volatile world.”

Labour had been hoping for more interest rate cuts from the Bank of England this year, to bolster consumer confidence and cut the cost of borrowing for businesses.

But with oil prices up above $100 a barrel and the key chokepoint of the strait of Hormuz still effectively closed, the Bank’s nine-member monetary policy committee left rates on hold at 3.75% at Thursday, and hinted they could even raise them, amid fears of resurgent inflation.