LONDON (Reuters) - A top MI5 officer said on Monday the security services could not have stopped the 2005 suicide attacks on London's transport system and that to suggest the agency failed to act properly was "nonsensical and offensive." "Witness G," who is chief of staff to MI5 director general Jonathan Evans, gave evidence anonymously to the inquests into the July 7 bombings. Families of the 52 victims were able to see him give evidence after the coroner, Lady Justice Hallet, ruled against him testifying from behind a screen. Reporters, however, were only able to hear his voice, from a nearby annex to the court. Witness G told the court the pressure the service was under from the sheer volume of plots it had uncovered, the number of individual "targets" it was monitoring and the lack of expertly trained staff it was able to deploy. He said resources had grown considerably since the 9/11 attacks in 2001 but that the agency still had "to prioritise ruthlessly." In a witness statement read to the court, he said the service "could only hit the crocodiles nearest the boat." To illustrate what it was up against, the court was told that in 2001 the number of militant targets being pursued was in the order of 250, rising to more than 500 by July 2004 and more than 800 by July 2005. Asked if he rejected the accusation that there had been significant intelligence failings, he replied: "I do." "It would be both nonsensical and offensive" to suggest the intelligence services did not take steps to prevent the attacks, he added. Nevertheless he expressed "profound regret" on behalf of the agency for having been unable to foresee the future intentions of 7/7 ringleader Mohammed Sidique Khan and accomplice Shehzad Tanweer who were seen meeting known extremists 18 months before the bombings. The inquest heard how officers had watched, photographed and followed Khan and Tanweer in early 2004 during their inquiry into other militants planning a fertiliser bomb attack, but had not fully identified them. Witness G said it was easy with hindsight to say this or that link should have been followed up, whether it be a training camp in Afghanistan or another militant group or simply in the frequency of a name. The court heard how Sidique Khan and variations of the name "Sidique" had cropped up seven or eight times in multiple operations. But in the end he confirmed the security services had no inkling of what was to befall London.