THE head of MI5 delivered a chilling warning yesterday that a biological, chemical or nuclear attack on the West by al-Qaeda is inevitable.

In a frank admission of the threat to Britain and other Western nations from the perpetrators of the September 11, 2001 atrocities, Eliza Manningham-Buller said that a terrorist assault using a “crude” device was “only a matter of time”.

The director-general of the service responsible for protecting Britain from such attacks revealed that it was known that “renegade scientists” had co-operated with al-Qaeda.

Ms Manningham-Buller, who has been in her post since October, said that the scientists had given the terrorist group some of the knowledge it needed to develop the weapons.

She said that she had been forced to conclude from the intelligence about al-Qaeda that “we are faced with the realistic possibility of some form of unconventional attack”.

She added: “That could include a chemical, biological, radiological or nuclear (CBRN) attack. Sadly, given the widespread proliferation of the technical knowledge to construct these weapons, it will be only a matter of time before a crude version of a CBRN attack is launched at a major Western city.”

Ms Manningham-Buller’s remarks, during a keynote speech at a conference on counter-terrorism at the Royal United Services Institute in London, went even further in giving warning of the likelihood of an unconventional attack than the predictions of a senior Whitehall official in December.

The official, a key adviser to the Prime Minister, gave a special briefing to journalists with the authority of Downing Street, in which he said that the real risk of a chemical, biological or radiological terrorist attack in Britain would come, perhaps in five years’ time.

He said that a conventional attack, using high explosives, was more likely. Although not inevitable, he acknowledged that a small al-Qaeda cell operating in Britain might be able “to get through”.

Ms Manningham-Buller agreed that it was wrong to be “unduly alarmist” and that “the bomb and the suicide bomber remain the most effective tool in the terrorist arsenal”.

She emphasised that the discovery of traces of ricin poison in Britain (during a police raid in North London in January) “demonstrates that interest in unconventional weapons”.

“The unconventional threat poses significant new challenges for government and society in general,” she said.

She did not say who were the renegade scientists co-operating with al-Qaeda, but evidence emerged in Afghanistan that the terrorist organisation, led by Osama bin Laden, was experimenting with crude chemicals. Subsequent evidence suggested that Pakistani scientists sympathetic to the al-Qaeda cause may have helped with technical knowhow.

Ms Manningham-Buller gave no indication that there was specific new intelligence about a plot to attack a British city. But she made it clear that she considered al-Qaeda a “potent and deadly threat”, despite the successes against bin Laden’s group since the war in Afghanistan.

She said that al-Qaeda was capable “of real harm to our way of life”.

“Terrorist attacks by al-Qaeda have inflicted large-scale civilian casualties and they have deliberately attacked ‘soft targets’. This is not just a war against the State and its representations here and abroad,” Ms Manningham-Buller said.

She added: “In the front line, alongside military forces, diplomats and government targets, are tourists and people going about their normal business. Al-Qaeda’s targeting demonstrates the vulnerability of sophisticated Western societies.”

The supply of potential terrorists among extreme elements was also “unlikely to diminish”, she said.

Ms Manningham-Buller was appointed to the top MI5 job after a career in the Security Service. In the late 1980s she was head of one of MI5’s international counter-terrorist sections, and was fully aware of the Islamist terrorist threat well before the attacks in New York and Washington.

She said: “The threat from international terrorism is with us for a good long time. If this is a war that can be won, it is not going to be won soon. Breaking the link between terrorism and religious ideology is difficult.”

Based on MI5’s threat assessment, Britain is on a “high” alert status, a level that has been maintained since the September 11 attacks because this country is seen as the closest ally of the United States.

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