By Brian Wheeler
BBC News politics reporter
The ongoing conflict in Iraq is the "single most important recruiting tool" for potential suicide bombers, an influential committee of MPs has been told.
London bomber Mohammad Sidique Khan appeared in al-Qaeda video
Panorama journalist Peter Taylor, who made a three part investigation of the "new al-Qaeda" for the BBC, said Prime Minister Tony Blair was wrong to suggest terrorists were just using Iraq as another excuse to commit atrocities around the world.
Mr Taylor told the foreign affairs committee that, in his view, this was "patently not true".
He said Islamist terrorists were using the situation in Iraq to "recruit, to propagandise, to fund raise, to train and also to plan and operate".
And it was his "understanding" that violent jihadist propaganda filmed in Iraq had been discovered by security services on lap top computers belonging to the 7 July London bombers.
It was "simple" for al-Qaeda to make videos of suicide attacks on coalition forces and post them on the internet for propaganda purposes, Mr Taylor told the committee - and there was nothing that could be done to stop it.
Mr Taylor said he had been "surprised" by some of Mr Blair's comments on Iraq and terrorism.
He told the committee: "Iraq is the single most important recruiting tool that they [al-Qaeda] have, no question about it.
Peter Taylor was grilled by a committee of MPs
"And when the prime minister made that remark 'it is nothing to do with Iraq, they will think of any excuse' I was surprised, because the prime minister has a very good record on countering terrorism and political violence.
"I was surprised to hear him say that kind of remark about Iraq, which is patently not true, in my view anyway."
Mr Blair has acknowledged Iraq is being used to recruit terrorists, but he has repeatedly insisted the roots of extremism are much deeper.
In July he told a news conference: "They will always have a reason and I am not saying any of these things don't affect their warped reasoning and warped logic as to what they do, or that they don't use these things to try and recruit people.
"But I do say we shouldn't compromise with it. We shouldn't even allow them the vestige of an excuse for what they do. I do not believe we should give one inch to them."
Referring to the 11 September attacks on the US, Mr Blair argued the threat of attacks on the UK were already present before the London bombings.
Mr Taylor, who had been asked to give evidence to the foreign affairs committee because of his expertise in the subject, said he was "depressed" by the situation in Iraq, which he believed could turn into "another Vietnam".
But he said British troops were doing a "remarkable job" in Southern Iraq and had to "stay the course", as they had in Northern Ireland, "otherwise the other guys are going to win".
The success of coalition forces in destroying the Taleban regime in Afghanistan had led to a change in the nature of al-Qaeda, Mr Taylor told the committee, with members reportedly being told to "return to their country of origin" and recruit "home-grown would-be jihadists".
But the dispersed nature of the network meant it was difficult for intelligence services to penetrate it.
Professor Paul Wilkinson, of the centre for the study of terrorism and political violence, at the University of St Andrews, agreed with Mr Taylor's assessment of Iraq and the terrorist threat.
He told the committee al-Qaeda was the biggest terrorist threat the world faced and more had to be done to win the propaganda war against it.
Although many terrorist organisations around the world shunned al-Qaeda, it had "no shortage" of potential recruits, he added.
It had built a loose "network of networks" which was active in at least 60 countries, making it the "most widely dispersed international network ever".
"So although they are dealing with fellow extreme Islamists, radical Islamists, devoted to the idea, the aims of al-Qaeda, they have still got enormous scope for recruiting many, many more people," Professor Wilkinson told the committee.
He said it would take a "long, long time to unravel this network" but he was "optimistic" that it could be done, because the al-Qaeda has "misjudged the effect of terrorism on the public".
But he said it could not be defeated by military means alone and urged a "higher class of intelligence" and better policing.
Copies of Mr Taylor's series The New Al-Qaeda have been handed to the committee at its request.