They said that an ongoing oil strike in Venezuela, the world's fifth biggest exporter, was already pushing up petrol prices.

And a war with Iraq could see the problem made even worse - particularly if production in neighbouring Saudi Arabia or Kuwait was affected.

Any rise in prices at the petrol pumps is likely to be seen over the next three of four months.

Military action

Analysts said the Venezuelan oil strike was likely to add 4p to a litre of fuel - currently around 72p.

There is a general anticipation that more general pressure for a price increase will arrive in the next three to four months Safeway spokesman

They think that military action in Iraq could add a further 5p to the cost of a litre.

Orrin Middleton, energy analyst at Barclays Capital, said: "If for any reason Kuwait or Saudi Arabia are affected, then I think we will see oil go up to $40 a barrel."

On Friday the price of a barrel of oil climbed to $30 - its highest level for 15 months.

Mr Middleton said: "If the strike continues and stocks don't build, we could see a massive spike in gasoline prices.

"And this would definitely impact motorists here as well."

Production cut

The oil strike in Venezuela is built around opposition to the country's left-wing president Hugo Chavez.

The action has cut oil production by almost three million barrels a day.

On Friday Mr Chavez claimed that his government had overcome the worst of the oil strike, which has crippled his country for almost a month.

But protests continued on the streets of the country's capital, Caracas.

There's nothing anyone can do about it Esso

Turning to the possibility of a war against Iraq, analysts said there would be little effect on oil prices if Saddam Hussein was quickly overthrown.

The Petrol Retailers Association, playing down fears of petrol price hikes, agreed.

"There is always oil price speculation when there is tension in the Middle East but that is not likely to be the case with Iraq," said director Ray Holloway.

"And there are other producers in the world who are just looking for opportunities to get into the market, so we'll be protected."

Shell said it had no immediate plans to raise oil prices, but would follow any increases by its main rivals.

'Barrier for drivers'

Esso said it had little option but to follow crude oil prices.

Manager of external affairs, Howard Forti, said: "What's going on out there in the big wide world, those are factors that effect the prices of crude oil and when the price of crude oil is affected then people who are retailing petroleum based products obviously get affected.

"There's nothing anyone can do about it."

A Safeway spokesman said: "There is a general anticipation that more general pressure for a price increase will arrive in the next three to four months."

A spokesman for motoring organisation the AA said increases pushing the price of a litre of petrol past 80p would cross the "barrier of tolerance" for drivers.