Government spies believe at least two terror networks are operating in Northern Ireland, as it emerged international extremists were exploiting loopholes allowing them to come to the UK on student visas.
A "risk map" has been drawn up plotting the main bases for radical cells across the UK, totalling up to 3,000 members.
Northern Ireland has at least two of the networks, containing around 30 people, although the biggest threat comes from the Midlands in England, where 80 groups have been identified.
Members are not all involved in plotting attacks but can become quickly radicalised, according to experts. It comes amid claims that international groups are exploiting weaknesses in laws that allow them to come to the UK as students.
Former Queen's University student Kafeel Ahmed was critically injured in the car bomb attack on Glasgow Airport last Saturday. He remains in hospital where he is being treated for burns to 90% of his body.
Police in India have seized a computer hard drive belonging to him to recover the hard drive and CDs that he left in the Indian city of Bangalore when he travelled to the UK in early May.
Ahmed is also believed the have links with Abbas Boutrab from Algeria, convicted two years ago by a Diplock court in Belfast for downloading information from the internet on how to blow up airliners.
Damian Green, a shadow Home Office minister, said: "If someone does not show up for their course and explain immediately, their visas should be cancelled at once. It's an appalling loophole that the Government has to deal with urgently."
A Home Office spokeswoman said: "We do not comment on security issues."