Sir Richard Dearlove, who retired last year as head of the Secret Intelligence Service, said the July 7 bombings that killed 52 London commuters did not amount to a "strategic terrorist event," the Daily Telegraph reported.

Dearlove, who was taking part in a debate on terrorism arranged by the London law firm Ashurst, said the July attacks on three subway trains and a bus "bore the characteristic of a locally planned and carried-out event".

However British officials probably had to conclude that "the clock is running on some much more dreadful events that could occur," the former MI6 chief said.

In the medium to long term, terrorists would have access through the Internet to "some quite frightening dual-use technologies," he said.

These had not yet been used in the context of terrorism, but Sir Richard thought that they would probably eventually be used.

"There is no question that bits of al-Qaeda would have been extremely interested in biological weapons technology, chemical weapons technology, radiological devices and, ultimately, nuclear devices," he said.

Dearlove expressed "some sympathy" for the government's approach to fighting terrorism through legislation, adding that there was "extensive complacency" in Britain about the nature of the terrorist threat.

Meanwhile, the Daily Mirror reported that all four July 7 suicide bombers were tracked by security services a year before they attacked London.

But the surveillance operation was ditched after intelligence officers decided there was nothing suspicious about their behaviour, according to sources quoted by the newspaper.

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