Bernard Lee as Henry Houghton

William Sylvester as Gordon Lonsdale

Margaret Tyzack as Elizabeth Gee

David Kossoff as Peter Kroger

Nancy Nevinson as Helen Kroger

Thorley Walters as Cmdr. Winters

Gillian Lewis as Marjorie Shaw

Newton Blick as P.O. Meadows

Philip Latham as Captain Ray

Cyril Chamberlain as Anderson

Justine Lord as Christina

Patrick Barr as Captain Warner

Derek Francis as Chief Supt. Croft

Hector Ross as Supt. Woods

Paul Eddington as Johnnie (uncredited)

Richard Marner as Colonel Monat (uncredited)

Geoffrey Palmer as Police Officer (uncredited)

Bryan Pringle as Surveillance Man (uncredited)

Andre Mikhelson as Russian Embassy Official (uncredited)

Garry Marsh as First Member at Lords (uncredited)

Basil Dignam as Second Member at Lords (uncredited)

Brian Nissen as Portland Official (uncredited)

Edwin Apps as Blake (uncredited)

Fred Griffiths as News Vendor (uncredited)

Anita West as Tilly (uncredited)