Public borrowing was worse than expected in July, the latest official statistics show.
In a blow for the government's deficit reduction efforts, the UK ran a surplus of just £1bn last month – £200m lower than July 2015.
The Office for National Statistics has also revised up its estimate for net borrowing in the last financial year to £75.3bn – £3.1bn higher than previosuly forecast.
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July’s figures are the first to cover the post-EU referendum period.
Borrowing for the 2016/17 financial year to date stands at £23.7bn – £3bn lower than last year.
Despite the worsening outlook, chief secretary to the Treasury David Gauke said the UK was “well-placed” to cope with the economic challenges ahead.
“With the public finances in surplus in July, our economy starts from a position of strength to face any economic turbulence following the vote to leave the EU,” the minister said.
“As we keep working to cut the deficit, we are well-placed to handle any challenges and seize the opportunities as our economy adjusts.
“We are determined to build on our economic strengths to ensure Britain is a country that works for everyone.”
Overall public sector net debt stood at £1,604.2bn, 82.9% of GDP.