A brutal robber who knocked an arthritic pensioner unconscious out-side a Marylebone library to steal his packet of Fruit Pastilles is behind bars.

Library volunteer Clarke May, 86, who walked with a stick, was left with a huge gash on his head after Abdi Mohamed knocked him unconscious on the steps of the Weiner Library in Devonshire Street.

The pensioner died on July 11, 10 weeks after the attack, from an unrelated condition. He had volunteered at the centre, which specialises in archives on the holocaust and Nazi era, for 20 years.

At Southwark Crown Court on Monday, Mohamed of Kipling Towers, South Acton, was sentenced to four years in prison after admitting one count of robbery.

The court heard that Mr May was climbing the steps to the library when he was struck from behind on April 23 this year. He fell to the floor where he was left unconscious.

The thug ran off with a bag containing Mr May's lunch of sandwiches, a packet of Fruit Pastilles and a newspaper.

A horrified witness called the police, and the pensioner was taken to nearby University College Hospital to be treated for a gash and bruises.

A second attacker, whom Mohamed refused to identify when he was interviewed by police, is yet to be caught.

In a victim impact statement, which was written before his death, Mr May said: "I suffer from very bad arthritis and I have done for some time.

"I walk with a stick anyway and the knock to my side made my condition worse.

"I suffered a cut to the head but this was glued, and I was in pain for several days and I have a small scar on my forehead.

"Because of this I was unable to go into central London to carry out my volunteer work at the library, which I have been doing for 20 years. I enjoy my work and I'm sad I couldn't continue for some four weeks."

Following his arrest, Mohamed was found to be drunk and tested positive for cocaine.

Passing sentence, Mr Recorder Dafydd Enoch QC said: "This was a nasty and callous robbery of an elderly man. You have built up an extensive record of violence and you are a cause for real concern to this court.

"While you have expressed remorse, you had little or no regard for the consequences of your actions at the time."