Author and actor Adrian Rigelsford was branded a "thief and a cheat" yesterday and warned by a judge that jail was inevitable after he was found guilty of plundering one of Britain's biggest picture libraries.

The 34-year-old, who ghosted biographies of the actors Peter Sellers and Brian Blessed, was a trusted visitor to the Associated Newspapers archive.

He told staff he was doing research and, because he was such a regular visitor, was allowed unfettered access to the huge collection. He repaid their kindness by smuggling out tens of thousands of often irreplaceable prints belonging to the publishers of the Daily Mail and Evening Standard.

Blackfriars crown court in central London heard that he then pocketed £75,000 from selling most of them to dealers.

Rigelsford - whose screen appearances include the role of an MI5 agent alongside Pierce Brosnan in the James Bond film Goldeneye - was unanimously convicted of stealing "in excess of" 10,000 prints between 1994 and 2002.

Judge Deva Pillay adjourned the case for four weeks for a pre-sentence report. Bail was refused. He told Rigelsford, of Huntingdon, Cambridgeshire that the courts had to send out a message that those who treated the "nation's heritage" in such a way would face custody.

Penny Rector, prosecuting, said Rigelsford took 56,000 photographs from the Kensington-based library, including turn-of-the-century shots of the British and Russian royal families, photos of the 1920s Irish Troubles, and a picture of the Yalta conference.

Some of the photographs were spotted in a shop in Charing Cross Road in 2002.

Miss Rector said Riglesford sold more than 30,000 prints for just under £60,000 to the shop and 26,000 for a further £15,800 to a second dealer. Only half have been recovered.

The author claimed he had retrieved the photographs with permission when they were thrown out.