This movie was in theaters only a few weeks after the publication of Len Deighton's novel. He had developed the subject as a novel and a movie project simultaneously, an idea that another best-selling author, Alistair MacLean, would soon take up with Where Eagles Dare (1968). Deighton was co-producer of this movie, as well as author of the novel, but is surprisingly not credited as author of the screenplay (which makes a significant change to the novel at the end of the story).
The prologue sequence for this movie is unusually long for a British commercial film of the 1960s - it's fully seventeen minutes before the credits appear.
This was the only feature film to give a screenwriting credit to the famous advertising executive John Salmon, one of the oldest friends of the film's co-producer (and author of the original novel) Len Deighton. Deighton and Salmon had been friends since they were schoolchildren together and Salmon had been a mentor to Deighton in his days in the advertising business.
The first feature film to give the subsequently-famous Anthony B. Richmond a credit as cinematographer; he was only in his mid-20s when the film was made, very young for a director of photography in those days.
The Beirut con involves a sum of £500,000. That would be at least £6 million in the present day (2022).