My Policemanis a forbidden love drama starring both Harry Styles – whose bid for movie stardom continues apace – and his naked bottom. The bottom is good. Ten out of ten for the bottom, particularly during a scene in Venice when the light from the window casts it in a golden, buttery glow. But otherwise, this is an average, meek and soporific endeavour which hits quite a few bum notes of the kind that aren’t ideal.

It is based on the novel by Bethan Roberts, which in turn was inspired by the romantic life of E.M. Forster, who had a long-term relationship with a married policeman who suffers a stroke and is nursed by his wife, May. (Big shout out for May, I think.)

The film takes place in two timelines, starting with Brighton in the 1950s when our policeman, Tom (Styles), begins to court a trainee teacher, Marion (Emma Corrin) but also embarks on a secret relationship with Patrick (David Dawson), a museum curator and older man who becomes a friend of both. Being gay was illegal: Tom needs to hide his sexuality and is mostly in denial about it – he jokes with his fellow police officers about ‘homosexuals’ – and this affair threatens to destroy them all.

Spool forward, and now we are in the 1990s, which will alternate with the first timeline. Here, Tom (now played by Linus Roache) and Marion (Gina McKee) are retirees still going through the motions of their milquetoast marriage when she, beset by guilt – you’ll find out why – offers to nurse Patrick who has, indeed, suffered a stroke. Tom, still in denial, wants nothing to do with him.

This Patrick is played by Rupert Everett, slumped in a wheelchair, although given that no one looks at all like their younger selves, the film could have gone the whole hogg and drafted in Mick Jagger, say? Or Paul McCartney. I’m only joshing. Morrissey?

This should be a Brokeback Mountain of a film. This should be a story of a time and place where two men are forced to give up the only great passion either one will ever feel. It should break your heart, but as directed by Michael Grandage, who is mostly known for his theatre work, there is no quiet accretion of mood to sweep you away and no sense of suppressed, pent-up emotion building until it can no longer be contained.

Instead, it is beset by cliché, especially when young Tom and Patrick take that trip to Venice and it’s a montage of gondolas and stolen kisses against honey stone walls and that naked bottom bathed in a golden light as a choir explodes with Vivaldi’s Gloria. It’s meant to be sexy but it just made me laugh and then I felt rotten, because this is so earnest. Brokeback did a lot more with less. (If memory serves, you see nothing and only ever hear the sound of a belt buckle being undone).

None of the characters, meanwhile, are richly drawn, plus there isn’t a squeak of chemistry between any of them. And Tom, in the later timeline, is seen walking his dog by the sea, over and over. Marion, in particular, is underwritten, though Gina McKee brings some heft by virtue of being Gina McKee. Styles, meanwhile, turns in a bland performance that never gets at what his character might be feeling. Whatever allure he has as a pop star isn’t evident here. I kept thinking: ‘Oh, Marion, just dump him.’