Public sector net borrowing was slightly lower than expected in September, at £14.138bn, down from £15.411bn in the same month in 2010.
The ONS said that solid growth in tax receipts and flat government spending were the cause.
So far this year government borrowing has reached £63.518bn, compared to £71.005bn at the same point last year.
The figures will give encouragement to the coalition government as it attempts to eliminate the budget deficit in the course of this parliament.
At the end of last month the national debt stood at £966.8bn, or 62.6 per cent of GDP, it was announced.
However, all these figures exclude the costs and revenues from the bailout of the financial sector, which the ONS consider temporary measures.
Once the full figures are given, the national debt stands at 147.6 per cent of GDP.