The 2012 Olympics in London will be a "huge target" for terrorists, the capital's police chief said yesterday.
His comments came after the Guardian newspaper quoted counter-terrorist officials as saying Britain had become the prime target for a resurgent and more structured al Qaeda.
Scotland Yard chief Sir Ian Blair told reporters: "There can be no doubt that the 2012 Games - if the current threat scenario stays the same - will be a huge target, and we have to understand that and work on that basis."
A team of officers was already working full-time on security, six years ahead of the Games, he said.
London was awarded the Olympics on July 6, last year, a day before four British Islamist suicide bombers blew themselves up on the capital's transport network, killing 52 people.
Police say they have foiled several other militant plots since that time, including an alleged scheme to use liquid explosives to blow up planes in mid-air between Britain and the United States.
As a close US ally with troops in Afghanistan and Iraq, Britain is a desirable target for al Qaeda and like-minded groups which accuse the West of waging war against Islam.
The Guardian quoted intelligence chiefs as saying al Qaeda had regrouped and grown more organised in Pakistan, despite a four-year campaign to track down its leaders.
It said experts feared Britain had never before been such a clear target, with groups plotting to conduct an atrocity on the scale of the September 11, 2001 attacks on the United States which killed nearly 3,000 people.
"They viewed 7/7 as just the beginning," one unnamed senior source was quoted as telling the newspaper, referring to the July 7 attacks last year. "Al Qaeda sees the UK as a massive opportunity to cause loss of life and embarrassment to the authorities."
Britain's traditional links with Pakistan made it a particularly easy target, with thousands of people travelling between the two countries each year, rendering it harder for the authorities to monitor security suspects, the Guardian said.
Officials also told the newspaper that groups in Britain were developing new structures, with a leader, a quartermaster in charge of acquiring weapons and conducting training, and several volunteers.
Scotland Yard's anti-terrorism chief Peter Clarke told the BBC last month the number of people the police needed to be "interested in" - not just terrorists, but those who support, encourage or assist them - was "into the thousands".
Scotland Yard launched a new counter-terrorism command this month, soon after Home Secretary (Interior Minister) John Reid declared that the country needed a "radical step change" in its security approach.