The National is about the last place you would expect to find a stage equivalent of a television soap opera - an Indian one, with a touch of Bollywood. That, though, is virtually what Ayub Khan-Din's amusing, farcical comedy about a young bridegroom who fails to rise to the occasion for six long weeks, at first proves to be.

Khan-Din has hit upon the idea of modernising All In Good Time, a forgotten, early Sixties comedy by north of England playwright Bill Naughton. Director Nicholas Hytner's production brims with social colour, but cannot disguise the fact that the hilarious comedy of morals and manners degenerates into an accusatory, confessional drama, with a happy ending imposed.

Khan-Din's thoroughly modern makeover does, I admit, enjoy a nice comic logic. When it comes to sex, and it takes just a few minutes to take the first of its sniggering, nudge-nudge appearances, the cultural affinities between Naughton's Sixties working-class family in Bolton and Ayub Khan-Din's 21st century Indian equivalents are revealed.

"Upstairs? Nothing's happened upstairs? In your bedroom? On your bed... You mean he hasn't got around to it yet?" the bride's mother, Lata, asks her wretched daughter, Rokhsaneh Ghawam-Shahidi's Vina. Each question betrays a nice combination of prudish embarrassment and consternation. It is characteristic of how everyone deals with sex - or the lack of it - in Rafta, Rafta. Almost nothing is said up front. Naughton's northerners suffered problems similar to those agitated Indians when up against the facts of life. Khan-Din, who made his name with the film East Is East, shows a flair for situation comedy but becomes strait-jacketed by Naughton's old-fashioned plot.

Tim Hatley's black and white photomontage of a Bolton terrace gives way to the cross-section of a two-storey interior, whose walls are painted in the style of an Indian restaurant. It is the wedding night of Ronny Jhutti's withdrawn Atul who has brought his bride, Vina, to share his life and upstairs bedroom-at his parents' house. Atul's father, Eeshwar, a jovial song and dance man with nimble feet and gesticulating hands in Harish Patel's effusive, not always intelligible performance, exudes exceptional bonhomie, while the marriages of Atul's parents and Vina's are soured by resentments. Eeshwar's wife, the wonderful Meera Syal, treats her husband to outbursts of brisk, withering contempt. When, after an over-protracted partying sequence the newlyweds head up to a bed rigged to collapse on them, you predict their first night will be nothing sensational.

Worse follows. After Vina reveals her virgin status and the four parents hold an impromptu conference, Rafta, Rafta should have parted company with Naughton and his plot contrivances. All In Good Time becomes fraught in its second half with outdated notions about homosexuality and Khan-Din retails them as if they remain current.

Not only does Eeshwar imply his son's love of classical music and reading are indicative of queerness, his wife retaliates by telling Vina's parents the story of her husband's intense relationship with an adored, long-lost best friend who accompanied them on their honeymoon. All this clichéd homoerotica is revealed only for it to be disposed of as an irrelevance, with Atul's marriage suddenly consummated and his parents reconciled. Rafta, Rafta hits its comic targets but peddles discredited and prejudiced fairytales about homosexuality. Thematically it beggars belief.