“These are the most difficult people to spot, especially if they are British-born.”A Whitehall source said: “What we cannot be complacent about is the possibility of previously unknown individuals acting on their own, perhaps inspired by the Iraq war or [Osama] bin Laden and the events of 11 September.”Last week’s attack was unique in several respects. It was the first suicide bombing by a Briton, the first by a foreigner in Israel and the first perpetrated by bombers travelling into Israel from Gaza after 89 previous attacks from the West Bank. All three factors minimised the chances of the attackers being intercepted before they carried out their mission.Before the 2001 attacks on New York and Washington, carried out by terrorists whose activities had passed virtually unnoticed by American intelligence agencies, MI5 was confident that it had rounded up all the active al-Qa’ida terrorists in Britain. Some have been extradited and others are in custody in Belmarsh prison, south-east London.Since 11 September 2001, MI5 has closely monitored about 30 people – most of North African origin – whom they suspect of close links with al-Qa’ida. They are ringed by supporters and active sympathisers, believed to number between 300 and 600.But Hanif and Sharif carried out their attack on behalf of Hamas, a Palestinian nationalist group which does not share al-Qa’ida’s vision of world Islamic dominance. Nor is Hamas known to recruit non-Palestinians, though Israel’s success in suppressing local suicide bombers may have led the group to change its policy.It appears, however, that the two Britons sought out Hamas.

This raises the spectre of a generation of young British Muslim men who have become more susceptible to targeting by extremists. The atmosphere, heightened by the September 2001 attacks and America’s response in Afghanistan and Iraq, has also been made more tense at home by campaigns against immigration and asylum-seekers, as well as gains by the far-right British National Party in last week’s local elections.In Sharif’s home town of Derby, Omar Abdullah, a spokesman for the radical Islamist group Al-Muhajiroun, whose meetings the bomber was known to have attended, said: “You look at everything that’s happened in the world in recent times, and of course there are going to be Muslims who are prepared to carry out attacks like this. “The passport could be a forgery.”But another resident disagreed, saying: “I can understand exactly why a young Muslim man would want to do what this man is supposed to have done In fact I’m surprised it hasn’t happened more. Since September 2001 the agency has nipped a number of planned terrorist attacks in the bud.But the Israel bombers are different. “How can the intelligence services monitor these kind of people in a democracy?” asked the Whitehall source “We don’t have mind control. MI5 are reliant on the person telling someone else, and that we are told about that communication.

And how do you distinguish between those who talk about doing something and those prepared to act?”Although Hanif and Sharif were taught by the British-based cleric Omar Bakri Mohammed, the self-styled “emir” of Al-Muhajiroun, terrorism experts do not believe they were recruited in Britain. “It is interesting that both men went to university in Damascus,” said Magnus Ranstorp, deputy director of the Institute for the Study of Terrorism at St Andrews University.”I suspect that was where they were identified by Hamas, which then exploited their idealism. They would have been talent spotted and then groomed.”There is a growth in the number of disaffected Muslim youth in Britain, and they will be exploited.”There have been radical clerics calling for the mujahedin to strike at Israel … and we are seeing a new kind of person becoming involved with the Palestinian cause.”Dr Ranstorp said the attack reflected “a worrying change of tactics” by Hamas, since it was the first time it had used foreigners, and believed that Hamas has been taking lessons from Lebanese Hizbollah in recruiting from Europe.