They can be absolutely confident that in the right conditions we would willing to use our nuclear weapons

Geoff Hoon, defence secretary

He also told MPs the possibility of terrorists acquiring weapons of mass destruction was a cause for "real anxiety" and something "we would have to guard against very seriously".

However, he stressed, there was no evidence that any terrorist group had so far acquired such weapons.

And the prospect of terrorists acquiring ballistic missiles was not considered a major threat.

Mr Hoon was briefing MPs on the threat posed by four countries identified by the UK as "states of concern" - Iraq, Iran, Libya and North Korea.

Chemical weapons

"There are clearly some states who would be deterred by the fact that the UK possesses nuclear weapons and has the willingness and ability to use them in appropriate circumstances, " he told the Commons defence select committee.

"States of concern, I would be much less confident about.

"Saddam Hussein has demonstrated in the past his willingness to use chemical weapons against his own people.

"In those kinds of states, the wishes and needs and interests of citizens are clearly much less regarded, and we can not rule out the possibility that such states would be willing to sacrifice their own people to make such a gesture."

No evidence

He added: "They can be absolutely confident that in the right conditions we would be willing to use our nuclear weapons.

"What I can not be absolutely confident about is whether or not that would be sufficient to deter them from using a weapon of mass destruction in the first place."

Mr Hoon outlined the risks faced

Of the four "states of concern" identified by the UK, Mr Hoon said North Korea appeared closest to developing intercontinental ballistic missiles.

There was no evidence of a direct threat to the UK from North Korea, he said.

But, he added: "Their threat is a threat to the stability of the world because they are clearly very determined to sell their equipment to anyone who has the cash to buy it."

Mr Hoon also singled out Libya as a cause for concern.

"I am sure Libya has an aspiration to develop a weapon of mass destruction and, equally, would like to purchase the necessary technology to allow it to deliver it.

"That conjunction is something we keep a close eye on."

Missile defence

Mr Hoon said he still considered Iraq the greatest threat the UK currently faced.

But, he stressed there were no states - to the government's knowledge - that had both the intention and the ability to launch an attack against the UK.

Mr Hoon refused to be drawn on the extent of UK involvement in the development of the US missile defence - or son of Star Wars - system.

The US has made clear that it wants to see territory of its friends and allies protected from emerging missile threats

Goeff Hoon Defence Secretary

In a statement, he told the committee: "We have so far received no requests for from the United States for the use of sites in the UK for missile defence purposes.

"We do not know exactly what might be involved in any such requests nor when they might be made.

"If we are asked to make such a decision we will ofcourse do so on the basis of our own national interest."

He said that would include the UK's own national security, which includes the "security interests of our closest ally".

"The US has made clear that it wants to see territory of its friends and allies protected from emerging missile threats.

"It has not yet said how this might be achieved. We are ready to engage positively in a dialogue on that question."