A 1.28p a litre rise in petrol tax will be imposed in October following a freeze because of the Iraq war, it is reported. In his Budget in April, Chancellor Gordon Brown delayed the planned rise because of the "high and volatile level of oil prices" caused by the conflict.
A Treasury spokeswoman told the Reuters news agency on Friday that the government had yet to announce whether the rise would go ahead.
But the Daily Telegraph said the Treasury had confirmed the rise would go ahead from 1 October, as the international situation had improved.
The paper quoted the shadow chancellor Michael Howard as calling the rise "another stealth tax" aimed at bringing a budget deficit under control.
However, analysts said the autumn tax hike would not affect motorists too badly, as petrol prices had dropped as Iraq began to recover its production.
Petrol in the UK currently costs an average of 76.2p for a litre of unleaded, according to the AA.
The motoring organisation said it was disappointed the rise was going ahead, as UK motorists already suffer from high taxes.
Duty makes up about three-quarters of the price at the pump for UK motorists.