Film: Life is sweet after all...Secrets and Lies Mike Leigh (15)

Mike Leigh's Secrets and Lies is a wonderful film, and a worthy winner at of the Palme d'Or; but it isn't very much like a Mike Leigh film, as we have known those things, from Bleak Moments in 1971 up to Naked in 1993. Gone is the self-conscious negativism, gone is the cold doctrinaire habit of caricature that used to put together a set of neurotic mannerisms and call the result a person. It isn't unprecedented for a Mike Leigh film to contain positive emotion - Life Is Sweet had a disconcertingly happy ending, one that might have been decided on at the last moment by the toss of a coin. But Secrets and Lies has a positive philosophy of emotion, and that is new.

That philosophy, spelt out near the end of the film by Maurice, is that secrets and lies are bad for people. "We're all in pain," he says, "why can't we share our pain?" This is virtually American in language and thinking, and sounds more like an inspirational address than an outburst from the character. But it has been built up to by a plot of great solidity, made of the hallowed ingredients of sentimental melodrama since Victorian times: an abandoned baby, dark secrets from the past.

Hortense (Marianne Jean-Baptiste), a young optometrist, applies after the death of her adoptive parents to learn the name of her birth mother. She is warned not to make her own inquiries by a social worker, Jenny (Lesley Manville), who represents the last gasp of the old Leigh: Jenny's mannerism is saying everything twice - "right, right", "good, good", "no, no", "yes, yes" - and she announces her caricature status by referring to the Guardian crossword. Only in a Mike Leigh film do people insist on the indicators of their allegiances like this, instead of just saying "the crossword".

Hortense points out what must be a mistake in the paperwork, saying her mother is listed as white while she is black. Jenny says there's no mistake. So Hortense and the viewer are prepared for the surprise of reunion, which is more than can be said for poor Cynthia Purley, the mother.

Hanging on Cynthia's kitchen wall is the dreaded "Green Lady" picture, traditionally used by art directors to mean "you may safely despise the person who not only bought this but hung it up". In this case the indicator is a double bluff, or else Brenda Blethyn simply refuses to make Cynthia, downtrodden and forlorn though she is, anything but sympathetic. If Cynthia has a mannerism, it is her wheedling use of endearment - "sweetheart" pronounced "sweedart" - but this may become a cultural craze in its own right, displacing "sweetie darling" from Absolutely Fabulous.

Blethyn's performance is also fiercely funny, not the comedy of embarrassment we associate with Leigh, but a comedy of distress. At the film's climactic barbecue, Cynthia is at one stage bent double with misery, but still urging her fellow guests to eat their cake. Cynthia can also be slyly exuberant: leaving the hairdressers with a smart new look, now that she's got something to live for, she passes her truculent daughter, Roxanne, a council employee, who is sweeping the pavement, and comes up with a line too good even to spoil by quoting.

Cynthia's sister-in-law is Monica (Phyllis Logan), who spends the money from Maurice's successful portrait photography business on keeping their new house immaculate. The Laura Ashley stencil that Monica is applying when we first see her is a similar signifier, in this very different world, to Cynthia's Green Lady: it says "feel free to hate this yuppie cow". Again, though, this is a false trail, and even if the character moves to a two-dimensional disclosure at the barbecue - a single fact explaining everything about her, as no one thing does in life - Logan makes moments of great pathos.

Secrets and Lies has a few of the mechanical moments of grace familiar from early films, where a character acts out of character - Roxanne's boyfriend, Paul, for instance, who has said virtually nothing, suddenly sides with his girlfriend's uncle against her. But the film has an unfamiliarly gracious understanding of the way people behave in different contexts. Back at work in the cardboard-box factory, Cynthia reverts to tremulous inadequacy when on the phone to her brother. Hortense, with her middle- class education, reins in any emotion when with her family of strangers, holding fast to her social manner. In one scene, her turmoil only shows when she gives her phone number to Cynthia and mixes up the digits.

Hortense is the character least explored by the film, and there is a risk of her being more a pretext for plot than a person. She only has a couple of scenes with a friend of her own, so it's good that they are so effective. She and Dionne are lovingly mocking their parents' generation ("Oh, lard!") and Hortense tries to be cool about Dionne's free-wheeling sex life, asking about condom use as if she was Dionne's parent.

Secrets and Lies is a beautifully constructed sentimental melodrama, with none of the rough edges that Mike Leigh has insisted on in the past. The only mystery is that Leigh should have come up with so classic a humanist product after proclaiming for so long that things could never be so simple.

One scene sums this up: Cynthia's first meeting with Hortense in a deserted cafe round the corner from Holborn tube at 7.30 on a Saturday evening. Mother and daughter sit side by side, so that the camera can observe both faces without cutting. It's a successful scene on its own terms, but Leigh is no longer asking the questions that used to be so important to him. Where in Holborn can you get a cup of tea at 7.30 on a Saturday evening? Why has no one else managed to find it? Where are the waiters hiding? Would two strangers really sit side by side rather than opposite each other, unless they were considering the camera's convenience?

On general release from tomorrow