Francis  Ford Coppola's The Conversation (1974), is a subdued, existential and ambiguous exploration of the limits of private and public responsibility as personified in the character of surveillance expert Harry Caul (a mesmerising, career-best performance from Gene Hackman) when he becomes embroiled in a conspiracy involving an unnamed corporation and its chief executive, the anonymous Director. The film becomes both a complex guessing game about the real intent of the two people who work for the corporation, Ann and Mark, that he has been hired to eavesdrop on as well as the gradual unravelling of Caul, an intensely lonely and pathologically private man. He finds his moral judgement, fueled by a refusal to become involved in the work he does and the repercussions of a previous surveillance job, questioned by the revelations on the sound recordings he makes of Ann and Mark's meeting in Union Square.

Caul initially believes, from listening to the surveillance tapes, that Ann (an ambiguous figure who could be the Director's wife or daughter) and Mark are attempting to cover up their affair from the corporation's Director (Robert Duvall). It is intimated that when he discovers their tryst he will kill them - "he'd kill us if he got the chance." However, when the Director's assistant Martin Stett (Harrison Ford) attempts to take delivery of the sound tapes in the Director's absence, Caul begins to suspect something more insidious and threatening. After a visit to a trade show for surveillance experts, where he again bumps into Stett, he invites his colleagues and two women back to his workshop. One of the women, Meredith, stays overnight and apparently steals the tapes at Stett's request. Harry decides to intervene in a hotel room rendezvous, as detailed on the tapes, and eventually discovers, contrary to what he had assumed from the tapes, that Stett, Ann and Mark have conspired against the Director and are about to murder him.

Euston Films, the subsidiary of Thames Television founded in 1971 by executives Lloyd Shirley (Controller of Drama), George Taylor (Head of Film Facilities) and Brian Tesler (Director of Programmes), recognised that British drama, at the time predominantly a mix of location filming and studio based video taping, could be made faster, cheaper and entirely on film. All three realised that the template of using lightweight film cameras, ten-day turnarounds with little or no rehearsal, non-union crews, and all-location filming -  the 'kick, bollock and scramble' approach coined by the crew of The Sweeney - would require some time to develop and establish.

The inspiration came from director Mike Hodges. Hodges's commitment to shooting and editing drama on 16mm film derived from his work on The Tyrant King, Trevor Preston's adaptation of Aylmer Hall's book as a serial for children, one of the first produced by Thames in 1968. He then wrote, produced and directed two television dramas on film for Thames Television under the 'ITV Playhouse' (1967-83) banner, Suspect (17/11/69 - Thames's first evening of colour programmes) and Rumour (02/03/70). Not only do they anticipate the development of Hodges's own style, a documentary aesthetic honed while working on Granada's World in Action (1963-98) and used in his seminal British crime film Get Carter (1971) that also influenced the creation of The Sweeney's pilot Regan, but it also proved to Shirley, Taylor and Tesler that their drive towards authenticity and realism could be produced without the need for a television studio and this particular way of making drama would make economic sense.