Rising crude oil prices could soon force petrol past the �4 a gallon mark, prompting calls on the government to cut taxes.

Motoring organisations are urging Chancellor Gordon Brown to re-think his forthcoming budget to ease the burden for motorists.

They warn that drivers on low incomes and in rural areas will be unfairly hit by the price hike.

Earlier this week, crude oil reached a nine-year high of $32 a barrel.

The rise is widely blamed on the Opec trade cartel, which has been accused of deliberately restricting the supply on its 40% control over the market.

Its knock-on effect is expected to be felt on the forecourts by summer, with prices pushing beyond the �4 mark.

According to the latest figures from the AA, the average price of petrol is now �3.46 a gallon, of which 80% is taxation.

The rises are likely to worry the government which is believed to be planning a tax rise in its 21 March budget to fund Treasury spending commitments.

AA spokesman Steve Upsher says the situation needs urgent action.

He told BBC News Online: "Motorists have been suffering high petrol prices for successive years now and the fuel tax escalator has taken fuel duty up to 80%.

'Crippling motorists'

"That's really the thing that is crippling motorists. They pay so much tax on their petrol with the price of crude oil going up it is out of hand.

"It might get to the stage where the government is very uncomfortable with the price of petrol.

Although the rise is likely to welcomed by environmental groups as a way of pricing out pollution, Mr Upsher says it will unfairly discriminate against those who can least afford it.

"It is the low income motorist that are hurt the most - along with people who live in rural areas of Britain.

"People have said in the past that driving is a luxury, but we say that, without a first rate public transport system, it is a necessity.

"It is another nail in the coffin for the motorist."