Petrol prices may be on the way up after the cost of oil jumped on the world market.
OPEC countries are due to rubber-stamp a decision to slash output by 1.5 million barrels a day at a meeting in Cairo.
Oil has tumbled on commodity markets due to lower demand after the September 11 attacks and a build-up of capacity among the world's major suppliers.
Non-OPEC members have agreed to follow OPEC's lead and news of the cutbacks pushed crude oil towards the 21-dollar mark at one point, a rise of 7%.
Garry Russell, coordinator of the Dump the Pump campaign, warned petrol prices in the UK could now rise to as much as 80p per litre over the next six months.
"2002 will see more heartache for people driving cars," he said.
"It's in the major oil producing countries' interest to restrict the flow of their product and I'm sure petrol prices will go back up again. The war against terrorism could spread further afield and this could have knock-on effects, with the Middle East becoming more unstable."
City experts dismissed the threat of impending price increases at the pump and said the impact of the production cuts on petrol would be negligible.
But supermarket chain Safeway admitted a sustained rise in the cost of oil on the world market would put pressure on them to pass on part of the burden.
A spokeswoman said: "If there is a sustained increase, there may be a need for us to increase our prices."
Shares in BP and Shell edged higher but neither would comment on the impact of the likely cut.