The film starred Humphrey Bogart and Ingrid Bergman and featured the song "As Time Goes By".
The 2m by 2m linen-backed sheet, one of only two known to exist, was bought by Andrew Cohen, the chairman of the door-to-door housewares retailer Betterware. Mr Cohen, who has collected film posters for seven years, said: "It's a great film and a great poster. The greatest poster ever produced."Reuse content