The Night Watch (BBC2)

Rachel Cooke is underwhelmed by a long-awaited adaptation.

I'm not sure that I understand the BBC's recent preference for the single film over the series.

Is it to do with money? Or is it increasingly scared of audiences falling away over a period of weeks? Either way, I think it's a folly. The BBC's long-awaited adaptation of Sarah Waters's The Night Watch (12 July, 9pm) - a story of love and loss, set in and after the London Blitz - was a case in point. It could have worked brilliantly, if only the person who commissioned it had been brave enough to insist on three hour-long episodes, one for each year that the novel covers (1941, 1944, 1947).

Instead, they wimped out and plumped for a single 90-minute film, with predictably underwhelming results. Paula Milne, its writer, must have felt as if she had been asked to cram a fur coat into a clutch bag.

It wasn't all bad. The atmosphere was superb: paste sandwiches, antimacassars, knitted tea cosies, horrible little moustaches, drawn on as if by a mascara brush. Not to mention illegal abortions, illicit sex and German bombs, all beautifully done.

Period authenticity is still the province of the BBC, as anyone who endured Downton Abbey on ITV1 will know. I also relished the way that excitement and a certain kind of camp poked through all the dreariness and hardship.

Waters is slowly inserting lesbians into all the times and places in which they were not previously allowed to exist. It's a joyous thing, well caught by the cast and director, Richard Laxton. I loved Julia Standing (Anna Wilson-Jones), the gay mystery writer, in her leather overcoat and wide-legged trousers, and her ex-lover Kay (Anna Maxwell Martin), suddenly coming alive as the Blitz licensed her to wear a tin helmet and drive an ambulance.

It would be hard to knock any of the acting. Jodie Whittaker was superb as Viv, a woman whose love affair had failed to whither, as it rightfully should have done, with the end of the war. So, too, was Harry Treadaway as her brother, Duncan, fresh out of the Scrubs. J J Feild gave Robert Fraser, Duncan's old cell-mate, a delightfully smooth veneer. His face shone like freshly mopped lino.

No, the problems were with structure, not surface. The Night Watch, like Harold Pinter's Betrayal, works backwards - the reader only fully understands events and even characters as he turns the final pages. However, unlike Betrayal, so short and snappy, The Night Watch is a slow burn.

Milne's many concisions squeezed out motivation and character, with the result that the story had a strangely soapy feel. I kept wondering why we were supposed to be interested in this interconnected group and their painful partner-swapping.

Was their sexual orientation alone supposed to hold our interest? It's possible. If everyone in the film had been straight, I doubt the film would have been made.

The biggest problem was Duncan's story. Even in the novel, his crime - it turns out that he was sent to prison for his part in a bizarre, failed suicide pact with a young man with whom he was in love - seems a little melodramatic (given the age, Waters could have successfully despatched him to the nick for a far less grave offence).

Here, with so little to explain it and so little in the way of build-up, it seemed baffling. A young man barged into the kitchen of the house Duncan shared with his father and Viv, muttering something hysterical about his call-up papers and how he wouldn't fight. Two minutes later, or so it seemed, he had cheerily slit his own throat. It was almost comical.

Nor was Duncan's relationship with Horace Mundy (a cameo from Kenneth Cranham), the prison officer with whom he went to live after his release, explored or even explained. How had this come to pass? Was Mundy secretly gay, too? Oh dear. It seems that we fans still await the perfect Waters adaptation (of her five novels, only The Little Stranger has yet to make it to the small screen).

I'm not holding my breath. It could be that she's just too good for the telly: too subtle and too clever by half. l