It appears to have been strictly a stage name, as he used the surname Heard on his marriage certificate in 1932, and there is no known documentation of a legal name change.
[1] Lorraine did his own stunts in movies, drawing on his natural strength and the physical skills he had developed prior to acting.
Examples of some of the daredevil stunts Lorraine performed include diving into a pool of sharks (filming on location in Jamaica), being thrown bound hand and foot from Walton Bridge into the river thirty feet below, fighting six men single-handedly and getting thrown down onto a table with such force that it splintered (this was an unrehearsed and unexpected thrill), jumping from an airplane, dangling from the jib of a very tall crane while bound, being dragged by a taxicab, and sundry chase scenes.
[1] Lorraine's acting career spanned three decades, and its end probably had as much to do with the near-standstill of the British film industry during World War II as with his advancing age for the types of characters he usually played.
Known as Lorraine Estates, it was initially involved in repairing bomb damage to property in Battersea and other sites in and around London.