Al-Qaida has become much more sophisticated and the UK is now its prime target, according to British counterterrorism experts.
British security sources told the BBC last week that al-Qaida had a network of cells in the UK, each with a leader, a quartermaster responsible for weapons, and volunteers.
The sources believe that five years ago al-Qaida consisted of several loosely connected organizations with common aims, but that it is now more organized, similar to how the IRA was set up.
According to the BBC report, terrorists are being trained in the UK and Pakistan and the July 7, 2005 terrorist attacks on London were "just the beginning."
Security officials are concerned al-Qaida is targeting universities and the Muslim community, and are less worried about recruiting from mosques.
Men in their late teens and early 20s are the main targets. Groups like the "Boy Scouts" are set up and then the volunteers receive religious indoctrination followed by political teachings and anti-Western rhetoric, according to the BBC report.
Next comes technical training and "bonding sessions," such as white-water rafting, and then the cell is ready.
BBC security correspondent Gordon Corera said the UK was vulnerable because "it may be easier for al-Qaida to strike the UK than other targets" as its leadership is based in the tribal areas of Pakistan, a country with close links to the UK and heavy flows of people in both directions.
He said, "It makes it easier to make the UK a target than the other countries it might wish to target. The leadership of al-Qaida does appear to have been regrouping and to be more coherent and organized than had been thought in recent years."
British security agency MI5 has set up joint regional offices for intelligence gatherers and antiterrorist police in Manchester, Birmingham and Sheffield.
London Metropolitan Police Commissioner Sir Ian Blair has said the 2012 Olympic Games in the British capital will be a "huge target for terrorists."
He said, "There can be no doubt that the 2012 games, if the current threat scenario stays the same, will be a huge target and we have to understand that and work on that basis.
"There is no question that hosting an Olympic Games in a liberal democracy rather than in China poses different issues."
The July 7 terrorist attacks took place 24 hours after London was chosen to host the 2012 Games.
The police chief said an assistant commissioner would be appointed to head security and that detailed plans were being drawn up that included the employing 30,000 security officers. All 200,000 workers involved in the games will be screened to see if they are security risks or working in the UK illegally, he said.
Assistant Commissioner Tarique Ghaffur, who is currently responsible for security but will hand over the job when a new chief is appointed, said the Metropolitan Police would carry out security risk assessments every three months.
"We will not tolerate criminal activity from those wanting to disrupt what is a major celebration for London, a showcase for London," he said.