In the 1930s he worked as a scriptwriter, most notably with Frank Launder on The Lady Vanishes (1938) for Alfred Hitchcock, and Night Train to Munich (1940), directed by Carol Reed.
While Launder concentrated on directing their comedies, most famously the four St Trinian's School films, Gilliat showed a preference for comedy-thrillers and dramas, including Green for Danger (1946), London Belongs to Me (1948) and State Secret (1950).
[2] He worked for a period as a journalist at the Evening Standard, later saying he was fired after refusing to interview a grieving widow who was too upset to be spoken to.
[4] Gilliat's early screen credits were on films directed by Walter Forde including Red Pearls (1930), Lord Richard in the Pantry (1930), Bed and Breakfast (1930), You'd Be Surprised!
Without Launder he did Take My Tip (1937) for Hulbert; A Yank at Oxford (1938) for MGM; Strange Boarders (1938); and The Gaunt Stranger (1938) with Sonnie Hale.
Gilliat, in fact, always deprecated his own comic talents, claiming that it was Launder who wrote all the jokes, though this was a huge overstatement.
But it was difficult generally to know where the contribution of one ended and the other began, even though officially they liked to take it in turn to act on each film as scriptwriter and director.
Launder directed I See a Dark Stranger (1946), Captain Boycott (1947), The Blue Lagoon (1949) and The Happiest Days of Your Life (1950).
Gilliat directed the thriller State Secret (1950) while Launder did Lady Godiva Rides Again (1951) and Folly to Be Wise (1953).
The film starred George Cole who later said working for the team meant "good scripts but terrible money.
Gilliat directed Fortune Is a Woman (1957), a thriller with Jack Hawkins while Launder did Blue Murder at St Trinian's (1957) and The Bridal Path (1959).
His obituary in The Times described his and Frank Launder's collaboration as 'one of the most sparkling writing, directing and producing partnerships in postwar British cinema.
'[3] According to one obituary "if wanted to give new generations, or foreigners, some idea of the way the British were in the thirties and forties, one could do no better than show them the films with which Sidney Gilliat was connected... [He] had unfailing good humour, and an unerring feeling for time, place and character.
[8] Another one said "Of all the tireless toilers in the ungrateful vineyards of British cinema comedy (Roy and John Boulting, Ralph and Gerald Thomas, Muriel and Sydney Box), Launder and Gilliat were least in thrall to the insatiable jokiness of the breadwinning professional humorist, and their long collaboration has left us with a memory of unfailing good-humour and an occasional brainy prankishness.