Being acclaimed as a cult classic can be a double-edged sword. Of course, it’s terrific to connect so strongly with any audience at all, but the down-side can be that the casual viewer feels the film ‘belongs’ to the die-hards, and huge swathes of people consequently give it the swerve. So it is with Withnail and I (1987): it’s adored by students and would-be bohemians, whereas other potential viewers suspiciously regard it as that one about failed actors in the Sixties that comes complete with its own drinking game. The whole issue’s a tricky knot for any study to untangle, especially as it’s sometimes unclear who the BFI’s guides are aimed at: do they seek to educate and enlighten, or to preach to converted devotees? Here Kevin Jackson makes a genuinely good fist of arguing the case for this unique film, gently highlighting its many virtues whilst keeping one eye on the brickbats of its detractors.

Interested parties have never had to look far to find a wealth of behind the scenes coverage of the production: besides the unexpurgated screenplay, a Bruce Robinson biography and Richard E Grant’s celebrated diaries, there’s a couple of exhaustive documentaries on the DVD. Nevertheless, Jackson unearths new revelations (who knew that a boozy, pre-fame Bill Nighy tried out for the role of Withnail?) Such background details are filled in alongside a thoroughly accessible scene by scene analysis of the feature itself. What emerges is a film driven by the pure strength of its script, richly comic and steeped in autobiographical inspiration, hand-tooled over many years before it went before the cameras. Such a promising screenplay could hardly fail, and the skills of the cast and crew – particularly the startling chemistry of the leads – lifted it to become one of the finest British films of its time – arguably, indeed, of any time.

By his own admission, announced to his crew at the start of the shoot, Robinson’s experience lay in writing (his screenplay for The Killing Fields (1984) was nominated for an Oscar) rather than directing, and so it largely fell to the other talents assembled by Handmade to translate the script into striking moving images. It may be the raft of beautiful one-liners that fans treasure the most, but the film also delivers many evocative images of Britain at the death of the Sixties, from seedy London to muddy Cumbria. Indeed, Withnail has a good deal of import to say about its time: not merely that of its setting, but also, indirectly, the Thatcherite joylessness of the mid- to late-Eighties. (Robinson’s subsequent form as filmmaker has been far less compelling, not least his follow-up How to Get Ahead in Advertising (1989), which unwisely sought to tackle rampant Eighties greed -as it were – head on. Still, at least he never made Withnail and I II…)

Jackson puts forward a very lucid, persuasive argument in favour of his subject, all the more so for simply illuminating what makes the film tick and allowing it to shine. It’s a brisk canter, but Withnail die-hards should find fresh facts to pore over, and less convinced readers may feel more open to being won over by the film’s peculiar charms. In celebrating it with sharp humour and unshowy intelligence, Jackson has done the phenomenon proud.