The robber forced an assistant to hand over cash at Thornton's Bookshop in Oxford, one of the oldest in the city.

The man, who had a distinctive mole below his eye, came in when the assistant was alone and ordered him to empty the till.

The terrified employee believed the raider had a weapon and gave him £110.

Thornton's was renamed Mr Harrison's for the show

A spokesman for Thames Valley Police said: "This was a nasty incident and we would urge any witnesses or anyone with information to contact us.

"At no time did the offender make any threat to the assistant but he feared for his safety as he believed the offender had a weapon."

The suspect is white and in his late 20s, 5ft 8ins tall and of medium build.

He has a mole on his left cheek and speaks with a local accent.

Scenes in the last ever episode of the detective series Inspector Morse were shot in the bookshop on Broad Street.

The store was renamed Mr Harrison's Bookshop for The Remorseful Day starring the late John Thaw and broadcast in November 2000.

Joseph Thornton opened his bookshop in 1835. Famous customers past and present include JRR Tolkien, Iris Murdoch, Michael Palin and Aung San Suu Kyi, the Burmese president elect.