The commercial success of Sweeney! the film ensured a sequel would soon follow. Though entitled Sweeney 2, the story here does not follow on from its predecessor and generally plays like an extended episode of the TV series, with a straightforward cops and robbers plot rather than a high-level conspiracy
The film starts in media res with George Carter (Dennis Waterman) in charge of an operation against a gang of blaggers, whilst his superior Jack Regan (John Thaw) has been called upon as a defence witness for his old boss, Jupp (Denholm Elliot), who is facing corruption charges.
As with Sweeney! Regan and Carter's usual boss, Haskins, is absent. His absence is less noticeable. For one thing his substitute Dilke (Nigel Hawthorne) occupies a similar role. For another the back-story between Regan and Jupp is both shown in flashbacks and proves relevant to the current case -- one that sees a rare failure for the Sweeney, along with the deaths of bystanders, hostages and blaggers alike, one of the latter being killed by his compatriots in a manner reminiscent of The Wild Bunch. (To reinforce the Peckinpah connection one of the robbers is played by Ken Hutchison of Straw Dogs.)
Notably we don't see all this, only the aftermath and Regan's encounter with the father of the hostage and learning that his regular driver, Big John, has had to have a foot amputated. This both gives Regan an additional personal stake in the case and results in the young, likely university educated, vegetarian Robert being assigned him, leading to some amusing culture clash interplay.
Regan and Carter's pursuit of the blaggers is complicated by the fact that they live in Malta, outside the Sweeney's jurisdiction. The gang are of comfortable, educated backgrounds and decided to leave the UK with their families because of their belief the country was finished.
Some nice rack focus and point of view
While these aspects of the writing work well and give the film a socio-political edge, the gang's modus operandi of always taking the same amount of money -- and thus leaving anything in excess of it -- and use of a sawn-off, gold-plated Purdey shotgun, seem gimmicky. (Just how do they take the gun in and out of the UK?)
A sense of padding out the running time is evident in a stand-alone sequence that sees Regan and Carter being called to a hotel where a bomb has been found. While perhaps reflecting the reality of being interrupted by unpredictable events, and topical, it felt too long to be throwaway but insufficiently developed to constitute a sub-plot to me. One thing this sequence does do, however, is present Patrick Malahide as one of the police involved with the case. Malahide was, after all, soon to become a regular alongside Waterman in Euston's next major series, Minder.
In sum, of interest if you like the TV series or 1970s gritty crime films.
A nice extended discussion of the film is here: http://www.thetvlounge.co.uk/sweeney/viewtopic.php?f=10&t=1579