The spook who's got Britain's legions of jihadists on the run Its success can be measured by the steady succession of terror-related trials that have taken place in Britain in recent years, with scores of al-Qaeda's followers sentenced to long jail terms. Plots to attack targets such as Heathrow airport and shopping malls have been thwarted, while MI5 also played its part in making sure last summer's Olympic and Paralympic Games passed without incident. The fact that Britain's legions of home-grown Islamist terrorists are finding it difficult to carry out attacks on home soil may well explain this week's revelation that hundreds of British Muslims are now travelling to Syria to take part in the jihad to overthrow President Bashar al-Assad's regime. While some have gone simply to assist with the deepening humanitarian crisis, intelligence officials believe the majority have joined Islamist terror groups. For years Pakistan's tribal areas on the border with Afghanistan were the favoured haunt for Britain's would-be Islamist terrorists, where they could learn their trade in making bombs and target-selection before returning home to carry out their missions. And while small numbers of British jihadis still continue to visit Pakistan, the prospect that the Free Syrian Army might actually succeed in overthrowing the Assad regime has inspired a new generation of extremists to focus on Syria. Rather than risk being apprehended and sentenced to lengthy prison sentences in Britain, the current generation of home-grown extremists are attracted by the promise of joining a cause that might actually succeed. But while this exodus of fanatics means they are - for the moment, at least - less interested in achieving their dream of martyrdom on the streets of Britain, the danger remains that, when the Syrian conflict ends, they will return home battle-hardened and primed to wreak havoc in British towns and cities. As Sir Jonathan himself warned in a rare public speech last year, Britain has experienced at least one "credible terrorist attack plot" each year since the September 11 attacks. Andrew Parker, MI5"s current deputy head, whose appointment as Sir Jonathan's successor was announced yesterday, will take comfort from the knowledge that recent changes to MI5"s modus operandi have greatly enhanced its ability to keep one step ahead of the terrorists. By the same token, he knows there is no room for complacency. As the July 7 bombings showed, all it takes is for one terror cell to fall off the surveillance radar for ordinary citizens to pay with their lives.