[4] The film stars Robert Donat, Sir Cedric Hardwicke and Margaret Leighton with Basil Radford, Kathleen Harrison, Francis L. Sullivan, Marie Lohr and Jack Watling (who was also in the original West End theatre production).

[5][6] Also in the cast are Stanley Holloway, Mona Washbourne, Ernest Thesiger, Wilfrid Hyde-White, Lewis Casson, Cyril Ritchard and Dandy Nichols.

An internal inquiry, which grants him no chance of defence, finds him guilty and his father, Arthur Winslow, is requested to remove his son from the college.

Unwilling to accept the verdict, Winslow and his daughter Catherine institute their own enquiries and engage a friend and family solicitor, Desmond Curry to assist them, including the briefing of the best barrister in England at the time, Sir Robert Morton, should the case come to court.

When the combined lawyer's bill reaches six-hundred and thirty-four pounds, well beyond his overdraft limit, the father is advised to cut his losses and abandon the case.

The play focuses on a refusal to back down in the face of injustice – the entire Winslow family, and Sir Robert Morton their barrister who represents them, make great sacrifices in order that right be done.

[11][12] According to Kinematograph Weekly the 'biggest winner' at the box office in 1948 Britain was The Best Years of Our Lives with Spring in Park Lane being the best British film and "runners up" being It Always Rains on Sunday, My Brother Jonathan, Road to Rio, Miranda, An Ideal Husband, Naked City, The Red Shoes, Green Dolphin Street, Forever Amber, Life with Father, The Weaker Sex, Oliver Twist, The Fallen Idol and The Winslow Boy.

[14] Writing in The New York Times however, Bosley Crowther compared the film unfavourably to the play, "staged with superlative finish on Broadway two seasons ago," but praised the "sparkling performance" of Robert Donat, and concluded, that despite these reservations, "the screen has a striking and an inspiring picture in 'The Winslow Boy'";[15] The Monthly Film Bulletin noted, "It is very much a period piece, in which the middle class, with its comforts, its unlovely interiors and hideous clothes, is very much in evidence.

It is too long, and would benefit by judicious cutting," although the reviewer concluded, "This is quite definitely a film to see and enjoy";[16] while more recently, Dennis Schwartz found the film to be "directed with great care for feeling and detail (the period settings are superb) by Anthony Asquith," and that it "proves to be excellent middle-class entertainment," and concluded by singling out Donat, "superb as the witty and elegant lawyer, who also has grit and compassion.