Kenneth Connor as Gregory Adams

Charles Hawtrey as Michael Bean

Leslie Phillips as Alistair Grigg

Joan Sims as Sarah Allcock

Kenneth Williams as Edwin Milton

Hattie Jacques as Grace Short

Rosalind Knight as Felicity Wheeler

Cyril Chamberlain as Alf Hudson

Ted Ray as William 'Wakie' Wakefield, the Headmaster

George Howell as Billy Haig - Saboteur

Diana Beevers as Penelope 'Penny' Lee - Saboteur

Jacqueline Lewis as Pat Gordon - Saboteur

Roy Hines as Harry Bird - Saboteur

Carol White as Sheila Dale - Saboteur

Richard O'Sullivan as Robin Stevens - Saboteur

Lorna Henderson as Pianiste

Diane Langton as Schoolgirl

Francesca Annis as Schoolgirl (uncredited)