Britain is now an inevitable target for international terrorists despite police success in thwarting previous attacks, Metropolitan Police Commissioner Sir John Stevens warned today.
His fears were echoed by London Mayor Ken Livingstone's grim forecast that it would be "miraculous" if the capital escaped attack.
Sir John also revealed that a team of Met police officers are in Madrid to see what lessons can be learned from last week's bomb blast to improve security at home. The number of dead rose to 201 today.
"Since September 11th, there have been 520 arrests, half have been charged with an offence and there are 90 about to go through to court," Sir John told press conference. "We do know that we have actually stopped terrorist attacks happening in London but, as the Prime Minister and Home Secretary have said, there is an inevitability that some sort of attack will get through but my job is to make sure that does not happen."
Police and security services are "working three times harder than ever" to foil any terrorist plot and the situation was constantly being reviewed. An extra 680 officers have been drafted in for the anti-terrorist operation and £52 million is set to be earmarked for the Met in 2004/2005.
But members of the public must remain vigilant in the current high state of alert as the Tube, trains, buses and clubs are possible targets, Sir John said.
Any terrorist will not find Britain an easy target, Sir John vowed. They will have to deal with some of the world's leading counter-terrorism measures which have been have been fine-tuned during 35 years of the Northern Ireland Troubles.
The warnings came as Spanish police say they are closing the net on the terrorists behind the Madrid blast and that Islamic extremists with links to al-Qaeda may be involved.
The Madrid terrorists may also be linked an attack in Casablanca, Morocco, last year that killed 45 people. One of five suspects being held by Spanish police, Jamal Zougam, had travelled to Morocco, then left on April 20th, 2003 - just before the May 16th attacks in Casablanca, according to officials in Morocco.