The unidentified middle-aged man was detained by armed officers after an extensive nationwide police and MI5 surveillance operation which also led to the arrests of seven people in the Alloa and Falkirk areas of central Scotland later yesterday.
The operation was being seen as a significant success of counter-terrorism efforts since MI5 took over the lead intelligence gathering role from Special Branch. In this case, it appears to have involved the special expertise of MI5's teams of 'watchers'.
Scotland Yard refused to disclose the suspected destination of the bomb, but buses from the stop in Cricklewood lead to all parts of the capital; IRA bombers have been known to use buses while carrying primed bombs.
There has been speculation that the IRA would mount an attack in or near the City of London soon to defy the traffic control measures installed earlier this month - against the wishes of Scotland Yard - after the Bishopsgate bomb. Police accept it is impossible to guard against small bombs carried on foot.
Last night, the man was being questioned at Paddington Green police station, west London. The seven people detained in Scotland, including two women, were being held in Glasgow but are expected to be brought to London for questioning soon.
Senior Scotland Yard and MI5 officers were said to be 'very pleased' with the arrests. The man detained in London is suspected of involvement in recent incidents, but is not believed to be an IRA planner or organiser.
The arrest took place at 9am in Crest Road, Cricklewood. Witnesses said armed police leapt out of a taxi which was blocking the road and ordered the man to lie down.
Leroy Boyles, a social worker who was driving past, said: 'They told him to keep his eyes on one of the officers and put his hands out by his side.' He said the man was white, quite portly, aged 45 to 55, and carrying a satchel over his shoulder.
Kypros Orphanides, 39, a shopkeeper, said: 'I heard the police shout to someone to get face down on the floor. Then another policeman came in and said 'Get out to the back of the shop, because there's a bomb outside.' '
Police sources said the man was carrying a bag containing several pounds of Semtex, a timing device and a detonator. The immediate area, including a number of shops and houses, was sealed off for several hours while the device was defused. It is believed that the man arrested does not live in London and had travelled to the area by car while under surveillance. A blue Ford Escort car parked near by was later taken away for scientific examination.
It is not clear why the police chose to move in when they did, but it could have been because of the difficulties of surveillance if the man had switched buses several times - a common IRA tactic to detect 'watchers'.Reuse content