What was the first British sound film?

"Blackmail" is a 1929 British thriller drama film directed by Alfred Hitchcock and starring Anny Ondra, John Longden, and Cyril Ritchard. Based on the 1928 play of the same name by Charles Bennett, the film is about a London woman who is blackmailed after killing a man who tries to rape her.

After starting production as a silent film, British International Pictures decided to convert Blackmail into a sound film during filming, becoming the first successful European dramatic talkie; a silent version was released for theaters not equipped for sound (at 6,740 feet), with the sound version (7,136 feet) released at the same time. The silent version still exists in the British Film Institute collection.

The film is frequently cited as the first British sound feature film. Voted the best British film of 1929 in a UK poll the year it was released, in 2017 a poll of 150 actors, directors, writers, producers and critics for Time Out magazine saw "Blackmail" ranked the 59th best British film ever.