The head of the Yard's anti-terrorism squad warned of "imminent" attacks by the IRA following the discovery of documents at the home of the Aldwych bus bomber, Edward O'Brien.
Commander John Grieve refused to give details of the find for security reasons but there was speculation last night that lists of targets and individuals may now be in police hands.
The announcement came after the discovery of a large amount of bomb-making equipment at O'Brien's home in Lewisham, south London. The 21-year-old was killed by his own bomb when it went off on a double-decker bus on the Strand, central London, last Sunday.
Commander Grieve said: "Following the discovery of significant quantities of bomb-making material and detailed documentation at George Lane, Lewisham, we are warning of the possibility of imminent attacks by the Provisional IRA on the mainland."
His warning, unusual for its timing and urgency, was backed by David Veness, assistant commissioner (specialist operations). He said: "Despite the recent activity of the anti-terrorist branch, we would encourage communities to remain watchful for further criminal outrages of any type, which may happen without warning."
Scotland Yard refused to elaborate on either warning last night, but senior sources have indicated in the past week that they expect more attacks, and that though there may be bombs elsewhere, London, particularly central London, will bear the brunt of the onslaught.
Detectives are understood to be concerned that the IRA has recruited a significant number of what they call "clean skins" - supporters with no previous known links to the republican movement. O'Brien fitted the description, but there may be some who are not even Irish.
"The IRA has been pretty active during the period of the ceasefire," said one senior source. "There may be car bombs, bag bombs, mortars or close-quarter assassinations. The full repertoire is available to them." He noted that preparations for the Docklands bomb must have been made long before the peace process ran into trouble at the beginning of the year.
Intelligence-gathering has led police to believe that the IRA now considers no target too sacred to attack. "In terms of 'spectaculars', they would like to hit anything that features on a postcard of London," said the source. "In other words, anything that would be recognised around the world."Reuse content