Watch for lone terrorists on the day, police warn

Scotland Yard said yesterday that lone terrorists unconnected with al-Qa'ida could use the anniversary of the 11 September attacks to commit their own bombings in Britain.

London will be ringed by roadblocks as security is stepped up before the anniversary, and extra police patrolling City institutions with links to the United States, underground stations and airports.

Anti-terrorist police warned people to be on a state of "alert but not alarm". The head of the Metropolitan Police's anti-terrorist squad, Assistant Commissioner David Veness, said there had been no specific threat to Britain and urged people to behave normally next week.

The security services and police will also keep Islamic extremists under surveillance. The undisclosed number of suspects represent what anti-terrorist officers believe is a small pool of support for extremist groups who could be capable of further attacks.

Mr Veness said the focus was not only on potential al-Qa'ida attacks, but those who might attack "because of the publicity it represents".

He said: "We shouldn't just think about the ghastly spectacular happening, but also the range of possibilities that smaller groups and individuals may use.

"There may be individuals who think here is an anniversary which is a world stage in terms of publicity and for their own reasons they might attack. We shouldn't underestimate these individuals."

Businesses in the City of London have been extensively briefed in recent weeks, as have other police forces across the country. Security will be in place for memorial events and Jewish holidays that fall over the 11 September period.

Mr Veness said "dramatic" progress had been made with counter-terrorism operations in the past 12 months. Since September 11, extensive work had been done on the threat posed by suicide bombers in Britain.

He said while public attention was on international terrorism the threat from Irish Republican dissidents was "not forgotten".

Since 11 September, Scotland Yard has received 8,000 requests for assistance from the Federal Bureau of Investigation. Mr Veness said: "By any comparison, this has been the busiest 12 months of counter-terrorism anyone can recall. Barriers have crumbled in the pursuit of the overwhelming public good."