A nervous newbie to the gay scene bites off more than a mouthful in this sweet and sadistic romantic comedy that plunges us headfirst into the world of BDSM. Pillion features an adorably boring parking attendant who meets an absurdly handsome biker hunk and become his submissive. Based on the 2020 novel Box Hill by Adam Mars-Jones, this is the likeable and accomplished debut of writer-director Harry Lighton which benefits significantly from the presence of Succession and Murderbot star Alexander Skarsgård as co-lead, a huge casting coup.

The film follows thirtysomething Colin (Harry Melling) who punishes illegally parked drivers, lives with his parents in Bromley, and sings in a barbershop quartet with his nice dad Pete (Douglas Hodge). One Christmas Eve, Colin is in his local pub on an underwhelming date organised by his terminally ill mum Peggy (Lesley Sharp, in a series of fabulous wigs) when he’s approached by a towering stranger, Ray (played by Skarsgård), at the bar. Ray orders three packets of crisps, one in each available flavour, and makes Colin pay for them, before passing him a note suggesting they meet outside Primark on Christmas Day. Colin can’t believe his luck.

Following an inept sexual encounter in an alleyway, Ray tells Colin that he has ‘an aptitude for devotion’, and so begins their very one-sided relationship, with a wide eyed yet up-for-it Colin surrendering his liberty and dignity for a crack at love. He shaves his head and starts wearing a lock on a chain around his neck, to which Ray has the key. Colin’s mum is understandably worried and confronts Ray about the apparently demeaning nature of their dynamic over a particularly awkward family dinner. His dad stays out of it. Colin is also inducted into Ray’s gay biker gang, which contains other couples enjoying similar arrangements. The group includes Kevin (Jake Shears of Scissor Sisters fame) who ends up as an annoying rival for Ray’s affections during a camping trip.

Pillion is a quintessentially British look at some out-there ideas which might seem small-time with its modest budget and unglamorous setting but is deceptively ambitious as it attempts to get to grips with what looks like an uncomfortable business (both physically and emotionally) and skilfully negotiates some significant shifts in tone. It balances quite explicit, sometimes squirm-inducing depictions of BDSM with Mike Leigh-esque domestic scenes; we watch as a lovable Hodge and increasingly no-nonsense Sharp are visibly bewildered by their naïve son’s new predicament.

If Ray maintains much of his mystery (beyond some spikiness and just a hint of sadness), Colin is presented as a fascinating mix; he seems to have little agency and not much going on in his life even before Ray takes advantage of that, yet he also has his limits, and his positive outlook and capacity for love and understanding is truly endearing. It’s a lovely lead performance from Melling, who may still be best known for his work in the Harry Potter franchise (where he played Harry’s dreadful cousin Dudley), but who has also impressed in the likes of The Queen’s Gambit and Wolf Hall. Meanwhile, Skarsgård’s preposterous attractiveness and movie star charisma are aptly out of place here, giving proceedings a fantastical dimension as you start to wonder whether Ray even really exists. It’s another well-judged performance from the Swedish actor, who seems to be getting better and better.

The film plays up the absurdism within this inarguably surreal social scene (which is made to seem particularly anomalous, and more amusing, within the suburban London setting). Lighton shows an eye for comedic compositions as the couple get stuck into some wrestling and open-air sexual shenanigans, and he picks out Melling’s priceless expressions, ranging from sore and startled to swooning and satisfied. The script is largely a triumph, too, from the simple but killer gags (the casual shouts of ‘wanker’ that greet Colin in his much-despised day job) to its fundamentally sensitive nature and thoughts on what might draw someone into this world. Pillion keeps its affability intact through some eye-watering exploits as it weighs up whether submitting totally to someone else’s wants can ever be ok.

Pillion is shown at BFI London Film Festival, Sunday 19 October; in cinemas from Friday 28 November.