A love letter to a cult music icon from a more famous fan, King Rocker is very British kind of rock documentary, loaded with irony and self-effacing humour. It is written and presented by Stewart Lee, a highly regarded stand-up comedian in Britain with a sideline as a music critic. Directed by Michael Cumming, King Rocker tells the colourful history of Lee’s friend Robert Lloyd, an eccentric indie rocker from the English Midlands who earned a small but devoted following in the late 1970s and 1980s, firstly with Birmingham punk band the Prefects, then with the Nightingales. In his post-punk heyday, Lloyd was something like a more charming cousin of The Fall’s notoriously fractious frontman, Mark E Smith: a charismatic, stubborn, proudly provincial working-class autodidact with a flair for witty, acerbic lyrics.

Blending archive footage of Lloyd’s early career with contemporary interviews and brief detours into lo-fi animation, King Rocker is an engagingly funny and personal film. In stylistic terms, it closely mirrors its subject: a self-mocking, sarcastic, wilfully amateurish celebration of the kind of DIY outsider artist who stoically carries on for decades despite minimal success. Lee’s high profile in Britain should ensure the film enjoys healthy domestic interest, even if Lloyd probably remains too obscure and culturally specific a figure to appeal wider global audiences. World premiering online as part of Sheffield Doc/Fest’s autumn programme, with theatrical and digital release planned for later this year, King Rocker will most likely find its main audience among middle-aged indie-rock connoisseurs.

The story begins with Lloyd’s early musical adventures on Birmingham’s post-punk underground in the late 1970s, where he rubbed shoulders with a young Duran Duran. His work with the Prefects and Nightingales soon earned critical approval from his rock peers, music critics and the legendary BBC radio DJ John Peel, who appears in King Rocker in archive clips. After launching his own independent record label from the back room of his local pub, the singer seemed to be destined for left-field pop fame. In the early 1990s, he was even briefly signed to the Virgin label as a solo artist, but they dropped him after one commercially unsuccessful album.

A disillusioned Lloyd spent most of the next decade in limbo, delivering mail in East London, drinking and gambling, struggling with money and mental health issues. But he reformed the Nightingales early in the new millennium, and the latest line-up continues to release albums and  play shows. A devoted fan, Lee has toured with the band in recent years, and clearly shares a warm friendship with Lloyd. The dishevelled pair certainly enjoy subverting the cliches of the rockumentary format, punctuating their rambling interviews with boozy laughter and surreal in-jokes about Birmingham rock history.

As well as interviews with Lloyd and numerous bandmates, past and present, King Rocker also includes brief cut-away cameos from famous musicians, actors, comedians and broadcasters who have crossed paths with Lloyd over the years, most notably John Taylor of Duran Duran. As a playfully absurd metaphor for the singer’s resilient spirit, Lee keeps returning to a statue of King Kong by Nicholas Munro that temporarily stood outside Birmingham’s main railway station in 1972. Since then, the giant gorilla has been moved to various locations around Britain, abandoned and restored numerous times. The Kong motif is a strained allegory for Lloyd’s chequered career, but both he and Lee clearly realise this, milking its absurdity for maximum comic potential.

Despite many decades of setbacks, long sabbaticals and health problems, the 61-year-old Lloyd remains musically active today. King Rocker could have been a story of failure, as the singer himself initially suggested, but instead Lee crafts it into a heart-warming tale of heroic endurance in the face of critical and commercial indifference. The pair make a ramshackle comedy double act on screen, a little juvenile and self-indulgent at times, but their charming little film ultimately feels like a long boozy conversation between old friends, full of deadpan humour and fond memories.