One prominent Conservative backbencher told the Independent that the authorities believed the IRA could be planning a political assassination, after the refusal of the Irish and Westminster governments to admit Sinn Fein leaders to the cross-party talks.
The security alert was tightened around some key targets whose names were discovered in the south London flat occupied by Edmund O'Brien, the IRA man blown up by his own bomb on a London bus.
The intelligence services in Northern Ireland have issued warnings about the general level of the threat from the IRA. But the failure to intercept the bombers whose Ford van, attracted a parking ticket two hours before it exploded, will raise questions again about the difficulty of cracking the cell network of the IRA network.
Ministers dismissed as "speculation" reports that there were three IRA active service units operating on the mainland, two in London and one touring the rest of the country.
But one senior minister said it had become clear that the IRA were improving their arsenal during the ceasefire when it was discovered that they had enhanced their mortar capability. Make-shift mortars were used in the attack on Downing Street. Now, the IRA are believed to possess mortars that can throw devices further and with greater accuracy.
The Manchester bombing was the seventh attack in mainland Britain since the ending of the ceasefire. The attempt in April to blow up Hammersmith Bridge with the biggest Semtex bomb found in this country, failed when the detonator did not ignite.
Northern Ireland ministers met informally at Westminster last Thursday to review progress in the cross-party talks. It was agreed that in spite of the rows, including the controversy over former US Senator George Mitchell chairing the key hearings, the talks were on track.
The Mitchell report, calling for "mutual" decommissioning, will be used to address the issue of loyalist paramilitary weapons, in the absence of Sinn Fein at the negotiating table. "There will not be a bonfire of weapons unless there is a double bonfire, with the IRA's weapons there too," said one Tory source.
Ministers reputedly had been ready to admit Sinn Fein to the talks had the IRA announced another ceasefire. But all the manoeuvring, some observers say, has been rendered academic by the Manchester bomb.Reuse content