Dirk Bogarde

as Sir Mark Loddon / Frank Welney / Number Fifteen

Olivia de Havilland

as Lady Margaret Anne Loddon

Paul Massie

as Jeffrey Buckenham

Robert Morley

as Sir Wilfred

Wilfrid Hyde-White

as Hubert Foxley

Anthony Dawson

as Gerald Loddon

Richard Wattis

as The Judge

Richard Dimbleby

as Himself