The Human Factor is a 1979 British neo noir film starring Nicol Williamson, Robert Morley, and Richard Attenborough, and directed and produced by Otto Preminger.

Maurice Castle (Nicol Williamson) is a well-bred, mid-level bureaucrat in MI6 whose life seems unremarkable, apart from the fact that he has an African wife, Sarah (Iman), and son, Sam (Gary Forbes).

Caught in a South African surveillance sting intended to compromise him into doing Muller's bidding, Castle fled the country to avoid arrest and exposure, then awaited Sarah – pregnant by a previous, then-deceased boyfriend – being smuggled to him by Connolly.

Ever since that time Castle has been repaying the favor by passing information on to the Soviets via a contact in London, and flinches when Muller casually drops that Connolly had recently "accidentally" died in police custody.

Shortly after he learns in an agency briefing given by Muller of a plan for the South Africans to use U.S.-supplied tactical nuclear weapons to eradicate the nation's Communist insurgents en masse.

Seeking to stay one step ahead of Percival and Daintry, he surrenders himself into the hands of underground Communist operatives in Britain, who successfully smuggle him to safety in the Soviet Union.

The two worst fates of which he can conceive – losing his wife and child, and not only forfeiting his career and nation but being coerced into representing himself as both a Communist and a traitor when he never intended to be either – close in on him like the jaws of a vice.

As with the book, much of the theme about alleged treason and suspicion is based on the defection of Kim Philby,[citation needed] a friend of Graham Greene, to the Soviets.