David Leppard and Abul Taher

Islamic terrorists may be targeting mentally disturbed or disabled people in Britain in a bid to form a new “brigade” of home-grown suicide bombers, security officials fear.

MI5 and police say the case of Nicky Reilly, who is being held over a nailbomb attack last week in Exeter, may indicate a new strategy of targeting vulnerable people with mental health problems to carry out attacks.

A counterterrorism official said MI5 was investigating the extent to which Reilly had been manipulated by a “charismatic” Al-Qaeda recruiter.

“It is a grotesque concept but they are using people who are clearly mentally subnormal,” the official said. “We know they have clever radicalisers who will take advantage of anyone they think they can manipulate, whether they have an IQ of 60 or 140,” he said.

Reilly, 22, is a Muslim convert who has spent time detained in a mental health hospital. He has been described as a shambling introvert with the mental age of a 10-year-old. He is believed to have Asperger’s syndrome, a form of autism, and may also suffer from schizophrenia.

Security officials say Al-Qaeda appears to have exported the tactic from Iraq, where disabled “foot soldiers” have been used to devastating effect.

They point to a case in February when a suicide bomber in a wheelchair killed an Iraqi general in Samarra, north of Baghdad. Earlier, two women, initially thought to have Down’s syndrome, acted as couriers for a bomb in Baghdad, killing almost 100 people.

Officials say people with mental disabilities are not only easier to manipulate but also less likely to arouse suspicion. If they are white Muslim converts, they are even less likely to be noticed.

The attack in the Giraffe restaurant in Exeter city centre on Thursday caught the authorities by surprise.

Police say Reilly – who is 18 stone, over 6ft tall and nicknamed the Big Friendly Giant – had three primitive but “viable” homemade bombs, which they believe he may have built using instructions on the internet.

One device exploded in the restaurant lavatory, leaving Reilly with severe cuts to his face. Yesterday police said he was in a stable condition in hospital.

Forensic analysis suggests his bombs were made from caustic soda, paraffin and nails in a tin box.

Police say that shortly before the explosion Reilly – who recently changed his name to Mohammed Rasheed – received a text message of encouragement. They are holding two men who were arrested at gunpoint outside an open-air cafe in Plymouth on Friday.

Security officials admitted that MI5 had been aware of Reilly but that he had not been under surveillance.