Anti-terrorist chiefs believe Saturday night's no-warning attack on a post office delivery depot in north London was an Easter "calling card" from the "Real IRA".
They have described the absence of warning as a "particularly worrying factor" in the tactics of the bombers, who showed a "reckless" disregard for the threat to human life.
Detectives investigating the explosion had no doubt that its purpose was to demonstrate that the "Real IRA" was "still in business". The incident will increase concerns in security circles that dissident republicans may seek to disrupt the general election campaign.
A device believed to contain between 1/2lb and 1lb of high explosives - similar in size to that used in the attack on Hammersmith Bridge last June - exploded at 11.28 p.m. on Saturday at the Hendon delivery depot near the busy Edgeware Road.
While awaiting confirmation from the forensics examination, the Deputy Assistant Commissioner, Mr Alan Fry, said he suspected it was the work of the "Real IRA".
Appealing to anyone who might have information to telephone the anti-terrorist hotline on 0800 789321, Mr Fry said: "The Edgeware Road is a busy thoroughfare, and there is a pub nearby. Whoever planted this device gave no thought to the consequences of their actions. This could have seriously injured someone. Due to the number of recent attacks, I suspect this is the work of the `Real IRA'."
The attack, which caused only superficial damage and injured no one, came just six weeks after the bomb blast outside the BBC Television Centre in west London. It coincided with an Easter statement confirming the "Real IRA" 's determination to continue its campaign against the British presence in Northern Ireland.
The BBC attack followed sustained warnings by Scotland Yard that the "Real IRA" was poised to escalate its terror campaign, with London its prime target. The device planted outside the BBC building detonated in a taxi as bomb disposal experts were attempting to carry out a controlled explosion.
Warnings of the BBC attack were telephoned to a London hospital and to an unnamed charity. They contained the same code word used to warn of last year's device on a railway at Acton, west London, also believed to have been the work of the "Real IRA".
Mr Fry said that no one was in the Hendon depot on Saturday night at the time of the explosion. However, he put the absence of casualties down to "luck" rather than terrorist planning.
Describing the absence of "any notice whatsoever" as a "particularly worrying factor", he said: "This is a residential area. Whoever put that device down was totally reckless as to someone living in the area, drinking in the pub just beyond this device, walking past at the time of the explosion, or in a vehicle, who could have had a serious accident."
Mr Fry did not know why the bombers had targeted the Hendon depot or what significance it could have had, if any, beyond being a post office building. However, the timing coincided with the commemoration of the Easter Rising and marked the third anniversary of the signing of the Belfast Agreement. Mr Fry also mentioned Friday night's television screening of Michael Collins.
"Whether any of these events featured in the planning, in the reasons behind this explosion, I don't know", he said. "Clearly, they are all lines of inquiry and all possibilities."
The Edgeware Road was closed and the area around the building was cordoned off yesterday as a forensic search of the area was completed.
Mr Gerry Madden, delivery office manager at the sorting office, said the depot would reopen as planned tomorrow morning. "Half a dozen windows were broken, nothing at all inside. Everything inside is perfect apart from a few scorch marks on the wall. No staff were due to be here until Monday night, when everything will carry on as normal", he said.
A fellow worker, Mr Jason Dale, said people were very shocked. "You expect them to target main post offices, not district ones. It's a little too close to home."
