Government borrowing in September rose to the third highest figure for that month since records began in January 1993.
Official figures show that borrowing – the difference between spending and tax revenue – reached ยฃ16.6bn last month.
The Office for National Statistics (ONS) said the figure was ยฃ2.1 billion more than September last year.
This is the last official set of public finance figures until the Budget next week, with the Treasury expected to change its own self-imposed debt rules.