Anthony Quayle's Oxford Dictionary of National Biography entry says that his first professional appearance, unpaid, was in The Ghost Train. The online article is here:
http://www.oxforddnb.com/view/10.1093/ref:odnb/9780198614128.001.0001/odnb-9780198614128-e-39947
For some strange reason the link occasionally shows the full content, even without signing in. If you aren't able to see it the first paragraph states:
"Quayle, Sir (John) Anthony (1913–1989), actor and theatre director, was born on 7 September 1913 at 2 Delamere Road, Ainsdale, Southport, Lancashire, the only child of Arthur Quayle, solicitor, and his wife, Esther Kate Overton. The Quayle family had Manx roots. During a rather lonely youth Anthony's interest in the theatre was encouraged by his lively and imaginative mother. He was educated at Rugby School and at the Royal Academy of Dramatic Art, where he stayed only a year. His first appearance on the professional stage, unpaid, was in The Ghost Train at the Q Theatre while on holiday from RADA. He began his career in earnest playing both Richard Coeur de Lion and Will Scarlett in Robin Hood at the same theatre in 1931."