Marley (15) / Salmon Fishing in the Yemen (12A) / Lockout (15)

One love – but many girlfriends

Every great artist deserves a great documentary. Martin Scorsese's epic bio-docs of Bob Dylan and George Harrison suggested as much, and Marley confirms it. Without having been a great fan or follower of Bob Marley and his music before now, I can't say precisely which information in Kevin Macdonald's film is new, but – narrated via unprecedented interviews with the singer's friends, family and close colleagues – it is comprehensive, absorbing and inspirational.

Marley was born an outsider, the son of a black Jamaican mother and an absent white father. His mixed race meant he was bullied by his contemporaries in rural St Ann's, where he was born, and in Kingston's Trench Town slum, where he grew up. One interviewee even blames his white genes for the melanoma that would eventually kill him. But as his fame grew, Marley transformed himself from an outsider into a unifier: of colours, of religions, of the rich and poor, of the opposing sides in Jamaica's horrifying political violence. When asked why he'd moved into Island House, the commune he created on the same street as the Prime Minister's residence, he said: "Sister, I bring the ghetto uptown."

The film doesn't shy away from his failings; Marley had 11 children from seven different relationships, and the painful effect of his infidelity on his wife, Rita, and her two children is clear. But Marley is more complex and admirable than most rock stars, and his music defies scepticism. There are 50 of his songs on the soundtrack and, at two-and-a-half hours, Marley is long for a cinema documentary. An earlier cut allegedly ran to four hours; if Macdonald were to release that version as a Scorsese-style BBC4 double bill, I'd gladly watch the lot.

Lasse Hallstrom's filmography, full of defanged adaptations of semi-difficult tomes such as The Cider House Rules and The Shipping News, is the cinematic equivalent of the Richard & Judy Book Club. Now he's adapted a book that actually was in the Richard & Judy Book Club: Paul Torday's 2007 comic novel Salmon Fishing in the Yemen. Dr Alfred Jones (Ewan McGregor) is an uptight civil servant and fisheries expert who is landed with the improbable task of transplanting 10,000 salmon to the Middle East on the whim of a fly-fishing Yemeni sheikh (Amr Waked) and the Prime Minister's press secretary (Kristin Scott Thomas) who's desperate for a good news story from the region. Jones is persuaded of the scheme's plausibility by the sheikh's comely business consultant, Harriet (Emily Blunt). In the desert, an unlikely – though predictable – romance blooms.

Films for the mum demographic tend to contain certain familiar elements: beloved British actors, understated love stories, international travel. The recent Best Exotic Marigold Hotel, for which Judi Dench and Bill Nighy held hands in India, was a fine example. But the plot machinery of Salmon Fishing ... turns too visibly to be convincing. The love triangle created by Harriet's dashing soldier boyfriend climaxes with a particularly crass plot twist, while the broad-brush political subplot stretches credulity like the daft Downing Street sections of Love, Actually.

McGregor, still twinkly and charismatic in early middle age, is miscast as a buttoned-up angler, though he becomes more believable with every button undone. Scott Thomas plays the PM's spin-doctor like a bowdlerised Malcolm Tucker, swearing gland amputated so as not to incur a box office-unfriendly rating. Thus, what might have been an interesting satire on the gulf between idealism and cynical political spin soon dissolves into chaste romantic sludge. But if it doesn't quite leap, then Salmon Fishing in the Yemen does at least float leisurely upstream on the strength of its stars' charm.

The credits for Lockout suggest it was developed "from an original idea by Luc Besson". But if you happen to have rented a lot of bad sci-fi B-movies in the 1990s, it ought to strike you as anything but "original". A high-security, low-orbiting space prison featured in the execrable Fortress 2: Re-Entry in 1999. And a rogueish criminal was sent to retrieve the President's daughter from the clutches of dangerous convicts in Escape from LA (1996). There are even shades of Seagal's Under Siege (1992) in the prickly flirtation between Lockout's rogue (Guy Pearce) and first daughter (Maggie Grace). As bad sci-fi B-movies go, it's cheap enough to be inoffensive, but not quite silly enough to be lovable. If an actor of Pearce's calibre craves some harmless fun, he could at least make sure a few of his character's incessant quips are funny.