Petrol supplies to Shell garages across the UK have been hit after hundreds of drivers launched a four-day strike in a long-running row over pay which union leaders warned will lead to shortages over the weekend.
Members of the Unite union employed by two companies on Shell contracts walked out at 6am and mounted picket lines which they said drivers from other firms refused to cross.
Prime Minister Gordon Brown urged both sides to resume negotiations, adding that contingency plans were in place to minimise disruption to the public.
Industry officials said there were no reports of panic-buying by drivers, one maintaining: "We are genuinely not seeing increased demand."
But there were reports of drivers topping up their tanks with small amounts of fuel or filling up spare cans, despite pleas from the government not to buy more petrol than usual.
Unite officials said the action was "solidly" supported and warned that the strike will have a worsening effect on supplies to Shell garages over the weekend.
At Shell's refinery in Stanlow, Ellesmere Port, pickets cheered when drivers not involved in the dispute turned their tankers around. The union said all 150 drivers on Shell contracts at the site were on strike.
In Plymouth, union leaders said the strike action had been joined by drivers from every company and fuel supplies in Devon and Cornwall could start to run dry by Friday night.
Unite joint leader Tony Woodley joined strikers on the picket line at Stanlow and said he was "bitterly disappointed" that extensive talks in the last two days had not resolved the dispute.
Sil Damhayan, who works at the Shell garage in Old Shoreham Road, Hove, East Sussex, said fuel supplies were running low as motorists had been panic-buying for the past three days.
PA