Ministers have clarified advice to motorists ahead of a possible fuel drivers' strike - telling them to refill tanks when half empty.

It came after government calls to "top up" tanks were blamed for panic-buying at petrol stations in some areas, with drivers ignoring calls not to queue.

High demand caused some garages to run dry but retailers said usual deliveries would ensure supplies were replenished.

Labour leader Ed Miliband called on the PM to apologise for the "shambles".

Some 90% of UK forecourts are supplied by about 2,000 tanker drivers in the Unite union, which is threatening a strike over their working conditions and pay.

Energy Secretary Ed Davey said people did not need to change their behaviour "very significantly".

"People just need to do the sensible thing if they're going into the petrol station. They should get a full tank of petrol, not a half-tank... and they should top up where necessary."

Calling the potential strike "completely wrong", he said it was important to prepare to ensure it did not "bring the economy to a standstill."

Ensuring vehicles had fuller-than-normal tanks was part of that, he said.

Running dry

Analysis Labour's call for a public apology from David Cameron is clearly an attempt to throw the political pressure over the fuel dispute firmly on to the government. But Labour probably don't need to try that hard as ministers seem to have contrived to throw themselves into the political firing line all by themselves. At one level Francis Maude's gaffe over jerrycans was bad enough. But it's over the issue of competence that ministers are most vulnerable. If voters and motorists form the view that the government has badly mishandled the situation, that will inevitably prompt questions about judgement. Worse, there is a danger their response prompts ridicule. Perhaps a period of silence from ministers on petrol (and pasties) would be a good idea.

On Wednesday, government advice that motorists should consider keeping their tanks "topped up" was criticised for stoking a crisis.

And a suggestion by Cabinet Office Minister Francis Maude that people store fuel in a jerrycan in the garage was later declared a mistake and withdrawn, after being condemned as potentially dangerous.

Teresa Sayers, chief executive of the Downstream Fuel Association representing retailers, said increased demand had resulted in some garages running out of fuel.

But she added: "It is a temporary issue and we are replenishing the fuel as quickly as we can."

On Thursday, Dorset Police urged people not to panic-buy and asked petrol stations to close where queues were causing a traffic hazard.

Oil giant BP reported increased demand across its sites on Wednesday, with individual tanks running dry but no garages running out of fuel altogether, while supermarket Sainsbury's said on Thursday "the vast majority" of its filling stations were open.

A poll by RMI Petrol, representing independent retailers, recorded petrol sales up 81% and diesel up 43% on Wednesday.

Rises of 45% for petrol and 20% for diesel had been reported on Tuesday amid talk of a strike.

Communications 'mishandled'

Edmund King, from the AA, said: "If drivers followed normal fuel-buying patterns there would be no fuel shortage whatsoever.

"We now have self-inflicted shortages due to poor advice about topping up the tank and hoarding in jerrycans."

Mr Miliband said strikes should be avoided "at all costs".

"That means getting both sides negotiating through [conciliation service] Acas today. Then David Cameron and Francis Maude should apologise to the country for the way they have handled this situation.

"And David Cameron should understand the lesson of this week: that he should start governing in the national interest not crude party interest."

Labour has accused the government of diverting attention from criticism of the Budget, while Conservatives have hit out at Mr Miliband for failing to condemn the stance of Unite - his party's biggest donor.

Chancellor George Osborne denied that motorists had been panicked by the government.

"The reason why people are concerned about fuel supplies is because we have a trade union threatening a strike that is potentially going to disrupt those fuel supplies," he said.

"The government has a responsibility to everyone in this country to take sensible contingency plans and the trade union has a responsibility to call off the threat of strike action - it is the last thing the British economy needs."

BBC chief political correspondent Norman Smith said ministers had suffered self-inflicted damage, mishandling the delivery of "common-sense advice" to create the very situation they were trying to avoid.

Expert advice

We could have calmed the whole situation down Brian Madderson, Chairman, RMI Petrol

No strike dates have been set, and Unite would give seven days' notice before any action.

Acas is attempting to convene talks between the union and seven companies involved in the dispute.

Unite, the UK's biggest trade union, has called for minimum standards covering pay, hours, holiday and redundancy for fuel tanker drivers.

Its drivers deliver fuel to Shell and Esso garages, as well as supermarkets such as Tesco and Sainsbury's.

RMI Petrol chairman Brian Madderson said the government should have sought industry advice "weeks ago" on how to avoid panic-buying and fuel shortages.

"We could have given them some good pointers... calmed the whole situation down," he said.

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