What nationality was the actor who starred with Trevor Howard, Sally Gray and Rosamund John in the film Green for Danger ? 
Scottish
Alastair Sim
Alastair George Bell Sim, CBE (9 October 1900 – 19 August 1976) was a Scottish character actor who began his theatrical career at the age of thirty, but quickly became established as a popular West End performer, remaining so until his death in 1976.
 He also appeared in more than fifty British films, starting in 1935.
Green for Danger (film)
Green for Danger is a 1946 British thriller film, based on the 1944 detective novel of the same name by Christianna Brand.
 The film was directed by Sidney Gilliat and stars Alastair Sim, Trevor Howard, Sally Gray and Rosamund John.
 The film was shot at Pinewood Studios in England.
 The title is a reference to the colour-coding used on anaesthetists' gas canisters.
Silent Dust
Silent Dust is a 1949 British drama/thriller film directed by Lance Comfort and starring Sally Gray, Stephen Murray, Derek Farr and Nigel Patrick.
 The title comes from lines in Thomas Gray's "Elegy Written in a Country Churchyard" "Can Honour's voice provoke the silent dust, or flattery soothe the dull cold ear of Death?"
 The screenplay was by Michael Pertwee, adapted from his own play "The Paragon".
 The film was shot in film noir style with dramatic use of light and shadow. Interpol (1957 film)
Interpol known in the USA as Pickup Alley is a 1957 British Warwick Films crime film shot in CinemaScope starring Victor Mature, Anita Ekberg, Trevor Howard, Bonar Colleano and Sid James.
 It concerns an Interpol effort to stamp out a major drug-smuggling cartel in numerous countries around the world.
 Victor Mature plays a US narcotics officer, with Trevor Howard as a drug baron.
 One reviewer described the film as a "feeble thriller", although it praised the performance of Howard. Rosamund John
Rosamund John (19 October 1913 – 27 October 1998), born Nora Rosamund Jones, was an English film and stage actress. Cafe Colette
Cafe Colette is a 1937 British thriller film directed by Paul L. Stein and starring Paul Cavanagh, Greta Nissen and Sally Gray.
 It was also released under the alternative title Danger in Paris.
 The film was made at Wembley Studios. Fame Is the Spur (film)
Fame is the Spur is a 1947 British drama film directed by Roy Boulting.
 It stars Michael Redgrave, Rosamund John, Bernard Miles, David Tomlinson, Maurice Denham and Kenneth Griffith.
 Its plot involves a British politician who rises to power, abandoning on the way his radical views for more conservative ones.
 It is based on the novel "Fame Is the Spur" by Howard Spring, which was believed to be based on the career of the Labour Party politician Ramsay MacDonald. Lightning Conductor (film)
Lightning Conductor is a 1938 British comedy thriller film directed by Maurice Elvey and starring Gordon Harker, John Lodge and Sally Gray.
 The screenplay concerns a London bus driver who becomes embroiled in a plot by foreign agents to steal secret documents.
 It was made at Pinewood Studios. Saturday Night Revue
Saturday Night Revue is a 1937 British musical film directed by Norman Lee and starring Billy Milton, Sally Gray and John Watt. Lady Behave (musical)
Lady Behave is a 1941 British stage musical which was written by Stanley Lupino with music by Edward Horan.
 Lupino starred alongside Sally Gray who had appeared with him in a number of films.
 Pat Kirkwood, Judy Kelly and Judy Campbell also featured in other roles during its run.
 It is set in Hollywood where a stuntman can't get his girlfriend to marry him until she has made a success in films.