Britain is now the main target of Islamic terrorists such as Al Qaeda
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.
Those involved in the cells 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 men in their late teens and early 20s, according to our correspondent.
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