Armed officers raided the home in King Street, Plymouth, connected to the man - named by police as 22-year-old Nicky Reilly.

Devon and Cornwall Deputy Chief Constable Tony Melville said Reilly appeared to be a "vulnerable" individual who had been "preyed upon" and "radicalised".

At a news conference yards from the Giraffe restaurant, Exeter, where the explosion happened just before 1pm on Thursday, he said: "Our investigations so far indicate that Reilly, who has a history of mental illness, had adopted the Islamic faith.

"We believe that despite his weak and vulnerable state he was preyed upon, radicalised and taken advantage of."

The £230 million Princesshay shopping complex, where the restaurant is situated, together with a number of shops and offices in the adjacent High Street, were evacuated for several hours while a massive police operation took place.

Reilly was arrested by police at the scene of the explosion, and suffered lacerations to his eye and some facial burning after a device exploded. Another device found in the vicinity of the restaurant did not explode.

The Deputy chief constable said: "Witnesses described how a male entered a toilet in the restaurant shortly before an explosion was heard." He said police and other emergency services went to the scene and the man was arrested in connection with the explosion.

Mr Melville said two explosive devices were made safe at the scene by bomb disposal experts, and were now being forensically examined.

"After the arrest, police searched an address in King Street, Plymouth, linked to Reilly using armed officers from the Tactical Aid Group," said Mr Melville. He said the premises were still being searched as part of the ongoing operation.