The Internecine Project

The Internecine Project is a 1974 British espionage thriller film written by Mort W. Elkind, Barry Levinson, and Jonathan Lynn, directed by Ken Hughes and starring James Coburn and Lee Grant. Set in London in the early 1970s, it tells the story of former secret agent Robert Elliot who is being promoted to a government advisor. To eliminate any ties to his past, Elliot devises and carries out a clever plan in which his four former associates will unwittingly kill each other on the same night.

Source: Wikipedia