About two-thirds into Sky Atlantic’s broadcast of King Rocker, Robert Lloyd – the subject of the film – is talking about how things were going from “bad to worse”. Unfortunately, an ad break comes in fractionally too soon and cuts him off; meaning what he actually says is “from bad to wor …” When the documentary resumes we have moved on, that final sibilant left unsaid. Probably forever. I’ve gone back and forth on this for ages, and I’m still not sure if it was intentional. It’s that sort of film.

This is, ostensibly, a documentary about a musician – Lloyd, the singer with 70s punk band The Prefects, which eventually morphed into cult Birmingham post-punk arty types The Nightingales. It tracks Lloyd’s hodge-podge career as he goes from art-rock frontman to record company boss, to band manager, to music video producer, to sit-com scriptwriter to pop solo artist, to replacing a sacked Nigel Slater as GQ’s food columnist despite never being a professional chef or restauranteur or, for that matter, a food writer. By the end of the film he’s once again the frontman of The Prefects who again transform into cult Birmingham post-punk arty types The Nightingales. These days he has an occasionally lucrative side hustle betting on horse races. You couldn’t, as they say, make it up. Was Lloyd actually good at these careers? Yes. Was he successful at them? And what does “success” even mean? That’s a different question, and one which King Rocker enjoys exploring.

Written and hosted by comedian Stewart Lee and directed by Brass Eye’s Michael Cumming, the film has fun playing with the conventions of rockdocs with their tales of success and excess, conveniently pat narrative throughlines and talking head inserts. In fact, if it wasn’t for Lee’s innate warmth and completely genuine love for Lloyd and his music, you would suspect that poking fun at the narrative conventions of music documentaries was the point of the whole thing. We even enjoy a trip to an ancient stone circle in Shropshire, presumably because after This Is Spinal Tap a music documentary without a reference to an ancient stone circle doesn’t deserve its place in the genre. Anyone familiar with Lee’s stand up will be unsurprised at his meta layering of themes; breaking out of interviews to comment on the nature of interviewing, pointing out when a handy metaphor presents itself and tee-ing up his subject’s best anecdotes while noting the artificiality and contrivances of doing so. There is, after all, no point using a narrative device unless you’re making your audience aware that you’re using a narrative device.

One such device is a huge, pop-art statue of King Kong that stood briefly near Birmingham’s Bullring centre in the early 1970s (“somewhere between Brian Eno leaving Roxy Music and Eddie Jobson’s first tour” says Lloyd), the weirdly incongruous local fixture, which was moved around the UK over the years and left to languish unloved before being restored to glory, being too good a metaphor for Lee to resist. The film cuts back to Lee doing a live reading on the history of the statue throughout, and wobbly animations of Lloyd’s adventures littered through the piece depict the singer as a giant ape. Lee, naturally, tells us very explicitly exactly what he’s doing here, but that doesn’t take away from its effectiveness in tying together the various narrative strands.

There’s a brilliantly playful grammar here, too, that harks back to anarchic and formative shows like The Young Ones: A reference to the Mancunian musician and journalist John Robb is followed by a blink-and-you’d miss it flash of the top of Robb’s distinctive head. He never reappears. Mentions of Duran Duran’s John Taylor, cookery writer Nigel Slater and 70s soft-porn icon Robin Askwith (one of the best moments here) are followed by cutaways to brief interviews, often accompanied by Lee saying “now we would cutaway to a clip of them talking”.

If all of this feels a bit on-the-nose and too-clever-by-half (not an uncommon accusation to throw at either Lee or Lloyd), it’s undercut by the sheer warmth the film has for its subject. It was Lloyd who suggested making a documentary, feeling that the almost-ridiculous evolution of his career could be looked at in the same way as such classic you-couldn’t-write-it underdog stories as Anvil: The Story of Anvil, but Lee disagreed. To him The Nightingales are a band worth celebrating unashamedly, rather than treating as a curio. His enthusiasm for the material powers the film far for more than his need to deconstruct the forms of documentary film-making. Quite right, too. Lloyd’s music, in all of its phases, is uniformly excellent. In fact, more on the music would have been nice– One of King Rocker’s very few shortcomings is that despite Lee’s obvious enthusiasm it would rather let the affable Lloyd spin stories than go deep on his artistic output. It’s arguably a sensible decision, since you suspect the initial audience for the film is more likely to be Stewart Lee fans than John Peel listeners or readers of the inkie indie press of the late 80s. Still, some more musical critique from occasional music-critic Lee could have added a shade more depth.

Lee and director Cumming also push a little harder than they need to keep the story moving. True, it skips along enjoyably; but some important beats are glossed over with what feels like undue haste (Lloyd’s stroke for example), and a reading of an unfilmed sitcom script, featuring comedians Kevin Eldon, Bridget Christie, Andrew O’Neill and Nish Kumar, is a riotous delight that could have gone much longer. It’ll be an extra on the Blu-ray with any luck.

Still, these are but quibbles. King Rocker succeeds partly as a deconstruction of the rockdoc form, true, but its real worth is as a lesson in not dismissing the outsiders, the also-rans and the nearly-weres, and the enduring appeal of cult bands and scenes that exist below the scenes of mainstream success.