Striking tanker drivers have threatened to call another four-day stoppage next week if no agreement is reached in the pay dispute that has threatened fuel supplies across the country.

The move comes as the Government instructed police forces to break up any picket lines that threatened to prevent tankers from leaving or entering fuel depots.

Emergency powers to order petrol rationing will come into force on Monday if the strike threatens to grow out of control. Any mass show of secondary picketing at refineries and distribution depots this weekend will disrupt plans by the industry to keep petrol flowing at the pumps. Fuel shortages will also be inevitable if farmers and hauliers join illicit protests.

Slow convoys of lorries will stage demonstrations today near refineries at Stanlow, Cheshire, and Fawley, near Southampton, over the high duty on fuel.

The Times has learnt that army personnel are not on standby to assist in a fuel crisis and have not been trained to load and unload the latest generation of fuel tankers. Ministers are banking on pledges from oil industry chiefs that there are sufficient fuel stocks across the country to last until the end of the strike at 6am on Tuesday, provided that motorists stick to normal buying habits. Nevertheless, officials at the Department for Business will monitor events over the weekend.

People appeared yesterday to be acting responsibly. Sales were 20 per cent higher than normal for a Friday and there were some queues at petrol stations, particularly in rural areas, but there was no evidence of panic-buying. Industry experts have said, however, that there could be local problems with some pumps running dry in parts of the Midlands and the North West, where other tanker drivers refused to cross picket lines or joined their colleagues in illegal action.

Shell has admitted that its network of service stations, one in ten of all petrol stations in Britain, will be affected by the strike and that some will run dry.

Emergency powers will be activated only if there is a sharp escalation in action that prevents tankers from maintaining normal deliveries.

The pay dispute involves 641 drivers who distribute fuel for Shell and are employed by Hoyer UK and Suckling Transport. The Unite union is seeking a 13 per cent pay increase and has rejected an offer of 7.3 per cent, backdated to January 1 this year, which would bring average wages to £39,000, and a further 6 per cent from January 1 next year, which would boost pay to an average £41,500. Shell drivers earn an average of £34,000, which includes one extra overtime shift a fortnight.

Negotiators from both sides last night were in touch by telephone seeking to reach a deal. Unite has served warning that it will call another strike from Friday next week if no agreement is reached.

Bernie Holloway, director of Hoyer, said: “We want to resume further talks and are therefore extremely disappointed that the union plans to strike again so quickly.”

It is understood that police chiefs have been ordered to keep the roads free from crowds to allow tankers to enter and return to depots throughout the strike period. Trouble is expected only at refineries or depots with one main entrance.

A BP spokesman was unaware of any problems regarding supplies. He said: “A lot of deliveries have got out and a number of terminals are working normally. We have strong stocks across the country. We are not asking our drivers to do anything that will compromise their personal safety.”

An oil industry source said: “We hope the Government does not need to call emergency powers and we think it could be an over-reaction. We think we have managed to get good fuel stocks around the country. The strike is for four days and against one brand. What signal would it send out if we had to use emergency powers for this? But it depends on motorists and if the dispute gets out of control.”

Unite made clear that the drivers’ grievance was only with Shell and that if drivers contracted to other companies were involved in secondary picketing, or refused to cross picket lines, it would be regarded as illegal action.

A spokesman said that informal talks were taking place by telephone and that negotiators were available for more talks this weekend. “We would hope that something might happen at the weekend.”

Shell said in a statement yesterday that its contingency plans were working well and that there were few reports of stations running out of petrol or diesel. A spokeswoman said: “Sales are high but not at extreme levels. There are very few signs of panic-buying. This may change, however, during the course of the strike.”

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