Al Pacino hits all the wrong notes as a rock warhorse looking to redeem himself in this weedy comedy

In 1971, John Lennon wrote to a young folk singer called Steve Tilston, after reading an interview in which Tilston had fretted that fame and fortune, should it ever arrive, would change his songwriting abilities for the worse.

The advice Lennon wanted to pass on was that it needn’t, and that success and credibility weren’t mutually exclusive. But between Lennon’s desk and Tilston’s door, the letter fell into someone else’s hands, and Tilston only received it 34 years later, when a collector of rock memorabilia got in touch to ask if it was real.

Danny Collins, the new Al Pacino film, imagines what might have happened if Lennon’s words had been meant for a singer who needed to hear them – one who was on the brink of selling out, and was silently begging for someone to talk him down from the ledge.

It’s an encouraging premise, and one which is squandered in every way imaginable by this weedy and entirely second-guessable comic drama. Pacino plays Danny as a superannuated sell-out, still plugging away at the stadium circuit with the same setlist that made him famous four decades earlier.

The Lennon letter is a birthday present from his manager (Christopher Plummer), and prompts an existential crisis. He puts his tour on hold and relocates to a chain hotel in New Jersey, where he reassesses his priorities, flirts with the general manager (Annette Bening), and tries to reconnect with his estranged son (Bobby Cannavale, from Blue Jasmine), daughter-in-law (Jennifer Garner) and granddaughter.

Who knows whether the writer and director, Dan Fogelman, is a fan of British comedy, but the whole thing has the air of the first series of I’m Alan Partridge, in which Steve Coogan’s light-entertainment grotesque shacks up in the Linton Travel Tavern following his high-profile sacking and divorce.

Pacino’s performance here is blaringly broad, and he feels fatally miscast as a pop-rock warhorse – his expansive gestures and roving monologues all shout actor rather than singer. At a push, his poise and wardrobe both owe something to Bryan Ferry – except then we come to his singing voice, which has more in common with the Rothesay ferry. There’s no gentle way to put this, but the melodies in Danny Collins are far from sweet, and imagining this man as having enjoyed any degree of musical success, however artistically compromised, is a stretch.

Danny’s signature song, Hey Baby Doll, is clearly modelled on Neil Diamond’s ‘Sweet Caroline’. But in execution – which, sad to say, is very much the word for it – it sounds more like S Club 7’s ‘Reach for the Stars’ played back at three-quarter-speed. Then there’s his ‘honest’ comeback number, a horrendous life-insurance jingle of a thing, which Danny slaves over for weeks without any noticeable signs of improvement.

As fans of This Is Spinal Tap, A Mighty Wind, and Walk Hard: The Dewey Cox Story know well, the dark secret of bad music in films is that it actually has to be good. But here, it’s never clear if Danny’s music is supposed to be quite as wretched as it is or not, which makes the character impossible to take seriously, and turns every performance into an uneasy punchline.

This matters because the film wants us to take Danny’s crisis seriously, and to hope that his relationship with his son – and perhaps also his flirtations with Bening’s prim nonentity – will work out for the best. But the moment every subplot grinds into motion, you know exactly where it’s off to, and the question of Danny’s redemption is never in doubt. The film is like an easy-listening ballad that finds its groove and sticks to it, and you sit there waiting for a key-change that never comes.