A fuel duty switch is reportedly being considered by Chancellor Philip Hammond in the run-up to the budget.
The move would see drivers of diesel vehicles paying more fuel duty, while the tax on petrol would be cut.
Mr Hammond is said to be under pressure from ministerial colleagues to deliver measures to slash dangerous emissions when he delivers his budget on November 22.
They believe increasing the tax on diesel might encourage drivers to switch to less polluting petrol vehicles, with the added incentive of a cut in duty at the pumps.
But there have already been protests from motoring organisations, who say the move would be unfair. Campaigners also fear it could damage business, with most lorries and vans running on diesel.
Fuel duties have been frozen in recent budgets. But the government still rakes in around £28bn a year from the nation's drivers, who pay around 60pc of the cost of each litre at the pumps to the treasury.
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