UK 'number one al-Qaeda target'
Al-Qaeda has become more organised and sophisticated and has made Britain its top target, counter-terrorism officials have told the BBC.
Security sources say the situation has never been so grim, said BBC home affairs correspondent Margaret Gilmore.
They believe the network is now operating a cell structure in the UK - like the IRA did - and sees the 7 July bomb attacks "as just the beginning".
Each cell has a leader, a quartermaster dealing with weapons, and volunteers.
According to our correspondent, each cell works on separate, different plots, with masterminds controlling several different cells.
They were often aware they were being followed and so were meeting in public spaces.
In addition, training is taking place in the UK and Pakistan.
It was thought that five years ago al-Qaeda was a number of "loosely-connected organisations" with common aims, but it is now more organised, she said.
Security officials are concerned the group is targeting universities and the community, and are "less worried" about mosques, she added.
The network is targeting "carefully selected" new recruits - mainly young Muslim men - according to the Guardian newspaper, which also quotes security sources.
The paper tells how recruits are then put through a "psychologically compelling" indoctrination of weekend and evening briefings.
This starts with religious lectures and prayer,
but moves gradually to more radical teachings and political discussions
about the position of Islam in relation to the western world.
He said these views were "based on activity they are actually seeing. Plots they're disrupting, trials which might be coming up soon".
"There is hard evidence behind it, rather than just theories," said our correspondent.
"That's based partly on what they are seeing, in terms of the types of activity, and partly based on the coincidence, that al-Qaeda's leadership is based in the tribal areas of Pakistan where there are links to the UK and flows of people going back and forwards.
"It makes it easier to make the UK a target than the other countries it might wish to target."
The network also appeared to be better organised, he continued.
"The leadership of al-Qaeda does appear to have been re-grouping and to be more coherent and organised than had been thought in recent years.
"The view is it clearly was an organised group before 9/11, but the campaign in Afghanistan disrupted that leadership very heavily."But in recent years, particularly in the tribal areas between Pakistan and Afghanistan, the al-Qaeda leadership has been able to re-group and re-organise itself.
"In doing so it's able to open up channels of communication, contact, recruitment and planning around the world, and operate those in a more coherent fashion than maybe we were seeing three years' ago."
However, intelligence analyst Crispin Black said another attack in the UK "was not inevitable", citing the UK's "considerable successes against the IRA".
He said the security services had a good idea about who they were dealing with, saying: "We still have that expertise and training present within our military forces and intelligence."
"It is no longer about looking for a needle in a haystack. We have some pretty good clues and information on where we should be looking."
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