The tale of Gloria Swanson as the doyenne of silent films whose career was ruined because she did not have the voice for talkies is refuted by a newly restored film.

The Trespasser, which will be shown at The Times BFI London Film Festival, demonstrates that Swanson was a multi-talented actress whose downfall had nothing to do with her ability to deliver lines.

Her performance, which includes an accomplished rendition of a love song, earned her an Oscar nomination in 1930 and led to several more talkies, but her career stalled abruptly because she made powerful enemies in Hollywood.

The myth that the talkies were to blame persists because of her portrayal of a faded silent-film star in Billy Wilder's 1950 classic Sunset Boulevard. Her character, Norma Desmond, also lost her star appeal when silents gave way to talkies.

Kevin Brownlow, the British film director, who interviewed Swanson in the 1960s, said that the real reason for her downfall was Hollywood politics.

Swanson, who died in 1983, took on the powerful studio heads by joining United Artists, a bold attempt by film-makers, including Charlie Chaplin, to control the distribution of their pictures.

“The men who ran the big studios were appalled when United Artists began,” Mr Brownlow said. “Richard Rowland, head of Metro, said that the ‘lunatics have taken charge of the asylum'.”

The furious studio men did everything in their power to undermine United Artists. Swanson, who had been earning $1,000 a week ($11,000, or £6,300, in today's money) with a bonus of $12,500 per film, soon found herself out of work.

She told Brownlow that producers had it in for her. “She was quite convinced there were conspiracies and racketeering going on. The Trespasser had its premiere in London and was a box-office success. Her voice was hailed as excellent for talkies.”

Reviews were mixed. Film Weekly announced: “Gloria has failed to bring it off.” But reviews in America were more favourable. Brownlow said: “It got very good notices in the United States, and she should have taken off as a talkie star. She made a total of six talkies before Sunset Boulevard. Everybody thinks that she was a great silent star and she reappeared in Sunset Boulevard, full stop. This is a myth.”

Clyde Jeavons, a former curator for the National Film and Television Archive, said that other silent film stars did suffer because of their unglamorous accents. “Clara Bow had a terribly strong Bronx acccent,” he said. “She made a couple of talkies, but did not have a good voice.”

Some actors had good stage voices that did not come across on film because primitive recording technology relayed some frequencies poorly, Mr Jeavons said. “Greta Garbo succeeded because she had a low voice. John Gilbert did not because he had a high tenor voice and he sounded tinny. Gloria Swanson had a good understated voice.”

Brownlow's study of 17th-century English radicalism, Winstanley, made in 1975, has also been restored for the London Film Festival.

Other film restorations in the festival include a version of Once Upon a Time in the West with 20 minutes of footage that was cut from the original release in 1968. Sergio Leone's epic western was crudely edited so that British and American cinemas could squeeze in more screenings.

Some footage had been restored for re-released versions, but key scenes remained absent until Martin Scorsese donated his personal copy of the film so that a full version could be made for the film's 40th anniversary.

The Trespasser will be shown at 6.15pm on October 29 at the National Film Theatre

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