As our comedians and satirists get older, they not so much get long in the tooth as lose them altogether; the bite, literally, goes out of the work.

Of the Pythons, only Terry Gilliam has retained his essential edginess and strangeness, whereas Michael Palin became a cuddly TV presenter and John Cleese a comedy Q. The Young Ones' Ade Edmondson was last seen presenting the hoary TV travelogue Ade In Britain. Just this week Peter Capaldi, best known as the ferociously foul-mouthed spin doctor Malcolm Tucker from political satire The Thick Of It, was named as Doctor Who - and Capaldi will definitely have to mind his Ps and Qs inside the Tardis.

And so we come to Alan Partridge, Steve Coogan's inspired poke at the narcissism and buffoonery of broadcasting, and a great comedy creation on first radio, then television. Alpha Papa is the first cinema outing for the character, and for many it is a triumph. It's certainly funny, sometimes laugh-out-loudly so, and good-natured, with the integrity of the character intact. Coogan and his writing partners aren't exactly pulling their punches. Yet at the same time, as a film it feels remarkably twee, as though the leap to the big screen diminishes a character who has roamed outside his natural, smaller habitat.

Alpha Papa sees Alan on the downward DJ slope, hosting Mid-Morning Matters on North Norfolk Digital, he and Sidekick Simon (Tim Key) hardly setting the airwaves alight with their inane quizzes and items such as "smells matter". It's an altogether shabby station, and when it's taken over by a media corporation, Partridge and his colleagues face the chop. But then night-time host Pat Farrell (Colm Meaney) takes matters into his own hands, by holding the station and his new bosses at gunpoint and drawing national attention to Norfolk.

The film is at its best when Alan is at his absolute worst - as when, his job slipping away from him, he attempts to save it with a brilliantly self-centred presentation to the board, complete with the line "wipe the prejudice juice off your hands" and the recommendation that they sack Pat, not himself; or when he sees an opportunity for advancement when the siege hits the national news. "Broadcasting live at a siege - at gunpoint," he croons, careless of the fact that his sidekick has a shotgun barrel taped to his head.

So he's as vainglorious, strait-laced, sociopathic and cringeworthy as ever. At the same time, one of the most satisfying aspects of Coogan's development of his best-known character, over 20 years, is the way Partridge's topsy-turvy career has been accompanied by a nuanced development of his personality; he's never been a static creation. And here, accompanied by the now greying hair (still appallingly styled) we can perceive tiny shards of humanity, even heroism, as he escapes with Pat on the road, literally broadcasting as a Roadshow, the police in pursuit being described on air as "slow-moving traffic on the A149".

But it's in these later stages, also, that the film's small-screen lameness becomes increasingly apparent. While Meaney beautifully balances Pat's comic idiocy and genuine, scary threat, other characters, notably the police, are paper thin. As such, the most I can give Alpha Papa is a B-.