His background provided Mankowitz with the material for his most successful book "A Kid for Two Farthings" (1953). This was adapted as a film by the director Carol Reed in 1955. Mankowitz himself wrote the screenplay. In 1958 he wrote the book for the West End musical "Expresso Bongo" which was made into a film starring Cliff Richard and Laurence Harvey the following year. Its director Val Guest suggested to Harvey that it might be a good idea to model his film role of Johnny Jackson on Mankowitz's own character, and so Harvey arranged a couple of lunches with the unsuspecting writer to study him at close hand, resulting in the character on film sounding something like Mankowitz. Mankowitz himself appears in the film's opening credit sequence, wearing a sandwich-board bearing his writer credit.