David Blunkett has rejected Conservative calls for a new security minister to coordinate the fight against domestic terrorism.

The shadow home secretary, Oliver Letwin, had on Tuesday backed the appointment of a senior political figure 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 to the UK 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.

And he 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".

Speaking to the same programme, the home secretary 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.

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

The Home Office also said the current arrangements work "very well".

"We already have a senior political figure with responsibility for domestic security and contingencies, namely the home secretary," said a spokesman.

"One of the most senior civil servants within Whitehall, Sir David Omand, is responsible for co-ordinating security and intelligence across government and reports directly to the home secretary."

The idea also came under fire from the Liberal Democrats.

The party's home affairs spokesman, Simon Hughes, said recent confusion pointed to poor communication rather than intelligence blunders.

"Of course, there is always an argument for reviewing the structure of government," he said.

"We have argued that there should be clarity in homeland defence structures, and that a cabinet minister should have overall responsibility for all aspects of the domestic response to terrorism.

"But duplicating US federal structures is clearly not the answer for the United Kingdom," Hughes added.

Public fears have recently been fuelled by a mistakenly released Home Office warning of a "dirty bomb" attack on London, threats to ferry services and Tony Blair's description of daily intelligence reports on terror threats.

There has also been criticism of media reporting of the arrest of three north African men on terrorism charges, following suggestions of a conspiracy to launch a cyanide gas attack on the Tube.