The claim, which is difficult to verify, was made by a highly placed source after criticisms of the police and the Security Service for failing to avert the Bishopsgate bomb in the City of London. It also comes in spite of conflict between MI5 and the police over disclosure of more details of the counter-terrorism effort.
Meanwhile, City of London Police disclosed that increased patrols since the IRA bomb at the Baltic Exchange last year had led to an overall reduction in crime of 10 per cent. Commissioner Owen Kelly also confirmed in his annual report that a man under arrest in Northern Ireland for other terrorist offences had been interviewed over that attack.
In the wake of the Bishopsgate bomb, senior police officers are known to be concerned at what they see as unjustified criticism of the counter-terrorism effort, which is sapping morale. But they believe to say more could risk giving away valuable information about police informants.
The senior source said: 'We have disrupted a number of attempts to bring bombs into London in the past 18 months. It runs into double figures. In addition to road blocks, we are doing a number of things in London about which we cannot be specific and which the public will not be immediately aware of. But at the moment we cannot disclose any more because some unguarded word, some snippet of information, is going to lead to the informant and someone is going to be dead as a result of it.'
Another reason why information about successful anti-IRA operations and counter-terrorism measures is being held back is the reluctance of the Security Service, which took over lead responsibility for intelligence gathering last October, to release information. The police source said: 'It is taking time to harmonise matters and it is working well. But there are huge cultural differences over the release of information. We just come from completely different standpoints.'
Each of the disrupted bombing attempts is understood to have been averted in the run-up to planting the device. 'As a result the IRA have changed tactics and keep changing them all the time. We can make no assumptions about the sequence of bombings since they will always try to wrong-foot the authorities.'
Senior police officers emphasised yesterday that a high state of alert will continue for some time since it is assumed that the IRA will attempt a repeat of the Bishopsgate bomb - or an equivalent - as soon as possible.
City police say they devote proportionately more resources to fighting terrorism than any other force.