Answer by taking a quote from the following article:

He was born James Lablache Stewart in Old Brompton Road, Kensington, West London, the only son of Major James Stewart, OBE and his wife Frederica Eliza (nee Lablache). Granger was educated at Epsom College and the Webber Douglas Academy of Dramatic Art. He was the great-great-grandson of the opera singer Luigi Lablache and the grandson of the actor Luigi Lablache. When he became an actor, he was advised to change his name in order to avoid being confused with the American actor James Stewart.

Granger's first starring film role was as the acid-tongued Rokeby in the Gainsborough Pictures period melodrama, The Man in Grey (1943), a film that helped to make him and his three co-stars - James Mason, Phyllis Calvert and Margaret Lockwood - into box office names in Britain.  Granger followed it with The Lamp Still Burns (1943) playing the love interest of nurse Rosamund John. More popular was another for Gainsborough Pictures, Fanny by Gaslight (1944), which reunited him with Calvert and Mason, and added Jean Kent. The New York Times reported that Granger "is a young man worth watching. The customers... like his dark looks and his dash; he puts them in mind, they say of Cary Grant." It was the second most popular film at the British box office in 1944.  Another hit was Love Story (1944) where he plays a blind pilot who falls in love with terminally ill Margaret Lockwood, with Patricia Roc co-starring. Granger filmed this at the same time as Waterloo Road (1945), playing his first villain, a "spiv" who has run off with the wife of John Mills. This film was popular too, and it is one of Granger's favourites.  Madonna of the Seven Moons (1945), with Calvert and Roc, was more Gainsborough melodrama, another hit. Also popular was Caesar and Cleopatra, supporting Claude Rains and Vivien Leigh; this film lost money because of its high production cost but was widely seen, and was the first of Granger's films to be a hit in the USA. At the end of 1945 British exhibitors voted Granger the second-most popular British film star, and the ninth-most popular overall. The Times reported that "this six-foot black-visaged ex-soldier from the Black Watch is England's Number One pin up boy. Only Bing Crosby can match him for popularity."  Caravan (1946), starring Granger and Kent, was the sixth most popular film at the British box office in 1946. Also well liked was The Magic Bow (1946), with Calvert and Kent, where Granger played Niccolo Paganini That year he was voted the third-most popular British star, and the sixth-most popular overall.

Did Granger work on movies during this time?
Granger's first starring film role was as the acid-tongued Rokeby in the Gainsborough Pictures period melodrama, The Man in Grey (1943), a film