Why MI5 now has UK's jihadists on the run

When Sir Jonathan Evans steps down as director general of MI5 next month, he can draw satisfaction from the dramatic transformation in Britain's ability to protect itself against the modern menace of Islamist terrorism that has taken place on his watch.

In April 2007, when Sir Jonathan replaced Dame Eliza Manningham-Buller as head of the Security Service - MI5's official title - the organisation was still reeling from the aftermath of the July 7 bombings in 2005, in which 52 civilians died and 700 were wounded. For MI5, the worst aspect of the attack was that it was caught completely off guard, even though some of the bombers had briefly been under surveillance.

Indeed, until the dreadful events of that summer morning, MI5's approach to tackling the emerging threat posed by Islamist militants was hardly reassuring. During the 1990s, when the service was consumed with existential debates over its post-Cold War role, it turned a blind eye as London became a world-renowned centre for Muslim extremists, resulting in its unwelcome soubriquet "Londonistan".

Even in the aftermath of the September 11 attacks, attempts to address the dangers posed by fanatical groups such as al-Qaeda were hindered by MI5's failure to track potential terrorist suspects, with the result that, on the eve of the July 7 attacks, Dame Eliza is said to have blithely assured senior MPs that there was no imminent terrorist threat to the country. As one senior MI5 officer later told me, "We were so unsighted about Islamist-orchestrated terror activity that they were effectively shooting at an open goal."

The fact that Britain has suffered no repeat atrocity on the scale of the London bombings is, in part, due to Sir Jonathan's attempts to address these defensive frailties. Having joined MI5 33 years ago at the height of the Cold War, when most of its work centred on hunting down Soviet spies and moles, Sir Jonathan has helped to remodel its operations so that its main focus today is to identify and disrupt Islamist terrorist plots. To ensure that MI5 never again allows key suspects to fall through the surveillance net, a significant proportion of Britain's annual pounds 2 billion intelligence and security budget has been spent on funding a substantial increase in its manpower and resources.

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.