(UK – Telegraph) – A terrorist attack on a major western city using a rudimentary radioactive device or biological and chemical weapons was “only a matter of time”, the head of MI5 said yesterday.

In her first public speech since taking up the post in October, Eliza Manningham-Buller said intelligence reports suggested that “renegade scientists” had given terrorist groups the information they needed to create such weapons and they had the ambition to use them.

The discovery of traces of the poison Ricin in London demonstrated their interest in unconventional weapons.

“My conclusion, based on the intelligence we have received, is that we are faced with a realistic possibility of some form of unconventional attack that could include chemical, biological, radiological or nuclear (CBRN) attack, she told a conference on counter-terrorism.

“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 is launched on a major western city.”

She said the “unconventional threat” posed significant new challenges for the Government and society in general.

“But before we become unduly alarmist, it is worth noting that the bomb and the suicide bomber remain the most effective tool in the terrorist arsenal.”

Miss Manningham-Buller also warned that the task of containing the al-Qa’eda terrorist network was difficult because it operated on a global scale and was impervious to political dialogue.

“If this is a war that can be won, it is not going to be won soon,” she said at the Royal United Services Institute.

“The supply of potential terrorists among extreme elements is unlikely to diminish. Breaking the link between terrorism and religious ideology is difficult in the short term.”

One problem was the incomplete nature and the sheer volume of the information that was picked up by MI5 and other agencies. She said that about 150 new pieces of intelligence about possible terrorist threats were received at the joint terrorism analysis centre at MI5’s London headquarters every week.

Although the two previous MI5 heads spoke in public, it is unusual for a speech to be made about ongoing operations rather than general policy matters.

Miss Manningham-Buller also responded to criticism that the security agencies dropped their guard before September 11 and did not take the threat from Islamists seriously enough.

A report from the Commons intelligence and security committee last year said: “The vulnerability of western states to terrorists with this degree of sophistication and a total disregard for their own lives was not understood.

“It would not be true to say we woke up to threat on September 12, 2001 . . . During the summer of 2001, Britain’s agencies knew that attacks, probably against US interests, were imminent. But their nature and target were unknown. What shocked us all was the scale and the devastation, which was beyond our imagination.”

However, she rejected suggestions that the intelligence and security arrangements needed an overhaul. The system worked and international co-operation had never been closer or more productive.