Downing Street has called on fire fighters "to change course" away from confrontation to compromise.

The plea came in the closing hours of the first in a series of strikes by Fire Brigades Union members.

Repeated calls for a return to negotiations follow top-level indications of a tougher government approach to an eight day walk-out set for next Friday.

"We are now coming towards the end of this 48-hour strike and there is one way for all this to be avoided and that is for the FBU to call off the strike, to change course," said the prime minister's official spokesman.

Ministers are warning the FBU that there will be no "political bar" to any action the government regards as necessary to guarantee public safety.

"I'm not closing any avenue. Things will be looked at," said the Number 10 spokesman.

Downing Street is to re-examine legal advice ruling out a court injunction to halt the strike.

"Issues that have been looked at and taken off the table will have to be looked at again," said the PM's spokesman.

"I'm not saying the answers will be any different but they will certainly have to be looked at again."

The government has confirmed that 15 red fire engines - usually used to train fire fighters - are to be used by troops.

And it has emerged that fire fighters will not prevent soldiers crossing picket lines in order to gain access to modern red fire engines.

Union leader Andy Gilchrist has given the green light to troops ahead of an expected eight day strike set for November 22.

The move follows a hardening government stance in a situation where modern equipment is trapped in strike-bound fire stations while the army struggles with its fleets of aging green goddesses."Fire fighters are neither prepared nor looking to hinder the armed forces," Gilchrist told the BBC.

The strike leader stressed that the barrier to progress was government intransigence.

"What we actually need is the government to free up the employers of fire fighters so that we can sit down and talk about a resolution around the take-home pay of £8.50 an hour," he said.

"It's a practical problem rather than us having a problem with the military, which we don't have."

Local government chiefs are also predicting that troops will cross FBU picket lines.

Sir Jeremy Beecham, chairman of the Local Government Association, said it would be a matter of judgement for military commanders and the government.

"I wouldn't welcome it but it may become necessary," he told the BBC.

"It's obviously going to be a matter of judgment for the government and the military."

"I only hope that the FBU do agree that in an emergency they will actually turn out, as they have done, in fairness."

But the FBU warns that replacing green goddesses with red fire tenders may have a "deleterious effect" on the strike's conduct.

Gilchrist: "Fire fighters are neither prepared nor looking to hinder the armed forces""I think it's a signal that the government were digging in for a long war of attrition with the FBU," he said.

"[It] will have an effect, a deleterious effect on what's happening."

Gilchrist has insisted that no deaths in house fires can so far be blamed of the fire fighter strike.

"Fire fighters have made an attendance at life threatening incidents and that will continue," he said.

"The statutory responsibility for fire safety and fire cover rests with fire authorities and indeed to some extent the government. They've had some six or seven months, and I find it a bit rich for them to be suggesting now that we talk about safety with literally minutes to go."

And the union leader cautions that breaking fire station picket lines could jeopardise the FBU's continuing - unpaid - involvement in emergencies while on strike.

"It will put even more strain on the kind of co-operation which has been shown by the FBU overnight in the tragedies that have taken place," he said.

A five-strong FBU fire crew broke the strike in a desperate bid to save the lives of four people who died in a Wiltshire.

The tragedy followed the deaths of four people in the first day of industrial action.