Iain Duncan Smith has challenged the prime minister to say whether the government is prepared for a major terrorist attack during a strike by fire fighters.

Quoting from a National Audit Office report, he said the NHS was not prepared for a major atrocity and called for the appointment of a new cabinet minister to spearhead the UK's response to the global terror threat.

During a lengthy exchange in the Commons, Tony Blair dismissed Duncan Smith's demand, saying the current security arrangements "work extremely well".

"It is extremely important that we make every preparation, yes, but it is equally important that we do not unnecessarily alarm people," said the prime minister.

But Duncan Smith said that there was "a lack of grip" and warned that the current arrangements would be "entirely unacceptable" should fire fighters mount an eight day walkout on Friday.

The Conservative leader warned the prime minister that he should use "the emergency powers at his disposal" to ensure public safety is maintained during any strike.

Blair said that the government had already proved that troops were able and willing to cover for fire fighters in the event of prolonged industrial action.

"In the event of a major emergency of course there is a procedure that will be maintained...fire strike or not," added Blair.

But the Tory leader said ministers had left a vacuum where intense contingency planning was required.

"People want to know why it is the government will leave it to the fire strikers to decide whether there is an emergency or not. The public want to know whether public safety will be put first," said Duncan Smith.

"Throughout all of this we've had different answers from different ministers on whether more money is available for the strikers, on the number of fire engines available to training."

Hitting back, Blair said that the Opposition was aggravating the situation "with an opportunism that is both as pathetic as it is transparent".

The clash came after the shadow home secretary, Oliver Letwin, backed the appointment of a senior minister to take the lead in protecting national security at a time of heightened risk.

Letwin argued that confusion and press scares over the seriousness of terror threats indicated the need for improved coordination.

He expressed concern at the lack of a "single weighty political figure" to take responsibility for all aspects of homeland defence.

The shadow home secretary told Radio 4's Today programme that cabinet ministers including the home secretary were too busy with other priorities to concentrate fully on the terrorist threat.

"I think the prime minister is right in saying that because we are rightly playing our part in the war on terror we are a target and right also to alert the public to the fact that this is a very serious difficulty," Letwin said.

"But if all of that is true then surely there ought to be someone who is full time on the job, who is very senior and who can look at all these things."

The shadow home secretary added that the new post could probably be created "without creating a vast bureaucracy".

David Blunkett rejected the suggestion, saying that any new department would cost hundreds of millions of pounds.

"There's nothing more dangerous than taking away direct accountability and responsibility from those who should carry it," warned Blunkett.

"Transport take responsibility for transport, underground, airports etc, health for health, local government for local government. They have to carry that responsibility."

Blunkett said that the relevant departments already report to him through coordinating committees.

"I chair both the key cabinet committees on resilience at home and of course the counter-terrorism cabinet committee. All senior ministers report into that," said Blunkett.

"I coordinate for the prime minister domestically as Jack Straw does with MI6 and GCHQ internationally."