The man, named by police as 22-year-old Nicky Reilly, suffered eye and facial injuries in the blast at the Giraffe restaurant in Exeter, Devon, on Thursday lunchtime.

Reilly, from King Street, Plymouth, has been in the Royal Devon and Exeter Hospital, Exeter, with police at his bedside, since his arrest at the scene of the blast in Exeter's £230 million showpiece Princesshay centre.

"He has not been formally interviewed," said a police spokesman.

It is understood that 6ft 1 inch tall, 18 stone Reilly has undergone an operation which is believed to have involved skin grafts.

Police are still questioning two men seized by armed police outside a cafe in Plymouth, Devon. One of the men was arrested when ten armed officers descended on the cafe, and another was detained to help with inquiries.

The police said inquiries are still going on at the Giraffe restaurant, and at the council flat where Reilly lived.

The bomb was made from sodium hydroxide and paraffin and packed with nails and was designed to detonate when it was shaken, sources said.

Reilly emerged from the Giraffe cafe "covered in blood" when the bomb failed to go off. Two other devices were found nearby. He had received a text message of encouragement before he left on the failed mission, sources revealed.

Police believe extremists took advantage of Reilly's low IQ and history of mental illness to radicalise him. He had changed his name to Mohammed Rasheed and had a screen saver of the Twin Towers in flames from the 9/11 attacks on his home computer, neighbours said.