The film followed DI Regan and DS Carter as they became embroiled in a deadly political scandal. One of the leading members of the British government, Charles Baker (Ian Bannen), is about to secure a huge deal with OPEC, stabilising the world oil market and boosting Britain's position within it. Baker is the rising star of the government, regarded as a future prime minister, and he is closely controlled by his urbane, manipulative American press secretary Elliot McQueen (Barry Foster).
When Regan investigates the mysterious death of a prostitute (Lynda Bellingham) as a favour to one of his informants, he becomes aware that Baker and McQueen might be involved. A spate of killings follow - which sees Regan take on both the criminals and the hierarchy of the Metropolitan Police and the British security services. The outcome of the film was similar to that of the Profumo affair, though with a typical Sweeney bittersweet ending.John Thaw as Detective Inspector Jack Regan
Dennis Waterman as Detective Sergeant George Carter
Barry Foster as Elliot McQueen
Ian Bannen as Charles Baker MP
Colin Welland as Frank Chadwick
Diane Keen as Bianca Hamilton
Michael Coles as Johnson
Joe Melia as Ronnie Brent
Brian Glover as Mac
Lynda Bellingham as Janice Wyatt
Morris Perry as Flying Squad Commander
Michael Latimer as P.P.S.
It was praised for capturing the spirit and setting of the original TV series. The film was successful enough for a sequel the following year, Sweeney 2, which saw some of the action relocated to the Mediterranean.
Announcing the sequel, Michael Deeley of EMI said the first film "was successful, so we're helping fill the demand by making another one".
Sweeney! was made by Euston Films, who also produced the television series. They had been planning a feature film version for some time: this movie was part of a £6 million six-film programme announced two years earlier, in 1975, by Nat Cohen of EMI Films.
The movie was released in 1977, following the conclusion of the show's third season on television, as a money-making big screen outing for what had become an extremely popular series. In the 1970s it was common for television shows to be given cinematic releases, amongst which were some of the biggest box office hits of the decade.
This was the second of three feature films based on the TV series. The first, Regan, an 80-minute made-for-TV movie which aired on ITV in June 1974, served as the pilot for the TV show, launching the first series off the back of its success.
A number of minor characters in the film had previously appeared in the television series. But Garfield Morgan, who played Regan's boss, Haskins, in the TV show (but who would be largely absent from the final season on TV the following year) did not appear. As with the television series, a large amount of the action took place outside the studio, with extensive location filming (as on all Euston Films productions). The film includes some nudity, and a great deal of graphic violence, which had been impossible to do for a television audience, hence the picture was released in the United Kingdom with an X-certificate rating (over-18's only).
The film follows fairly closely the events of the Profumo Scandal which had rocked British politics more than a decade before, although the film has a much more violent premise. It was also notable for featuring the topical subjects of energy policy and oil usage, major international issues at the time the film was made.