Commander John Grieve, head of the anti-terrorist branch, issued an appeal for information about the 7.5 tonne Ford Iveco lorry, which the IRA might have used to bring bomb components to the mainland.
The appeal follows a search on Monday this week of a north-west London lorry yard, which Commander Grieve said had been "clearly used by the Provisional IRA."
The vehicle, white with blue curtain sides, probably had a 1986 or 1987 registration plate (C, D or E), has red bars under the platform and a red bumper, and bears the remnants of faded sign writing on the cab doors.
Both Commander Grieve and the Metropolitan Police Commissioner, Sir Paul Condon, urged people in London to be on their guard against a possible Christmas and New Year bombing campaign by the IRA.
Sir Paul said his force remained on a high state of alert for a full range of possible IRA strikes, including bombings and incendiary attacks on stores during Christmas and the January sales.
Commander Grieve said the Ford lorry had been in the north London area earlier this year. Scotland Yard issued a computer-generated image of the vehicle.
"We believe the lorry was used at some stage to transport bomb-making equipment, possibly innocently," Commander Grieve said. "On the other hand, it may be part of the terrorists' transport."
The search of the lorry yard was carried out after information from the public and with the co-operation of its owners. Commander Grieve appealed for information from anyone who thought they had seen the lorry since February but said he was particularly interested in its movements in June and July.
He said the lorry might have been hired or lent out by an unsuspecting owner. No explosives or firearms had been found at the lorry yard, and there were no arrests.
"We are appealing to members of the public to help us trace this lorry. It is communities that defeat terrorism and this is a task everyone can help us with," Commander Grieve said.
He appealed to anyone who had seen the lorry, owned it, had bought or hired it recently or seen it parked to ring the free and confidential Anti-Terrorist Branch hotline on 0800 789321.
"It is by making London as hostile and environment as possible that we have the best chance of success," Sir Paul said.Reuse content