LIFE IS RARELY SWEET

In 1993, Mike Leigh won top prize at

Cannes for 'Naked'. This year, his new

film is once again the leading British

contender. Lately though, it hasn't only

been his work that's attracted attention

Mike Leigh explained his philosophy of comedy to me by patting his paunch. "I'm over-eating," he said, "over-indulging my tummy. That's why our production company is called Thin Man Films."

Fat men are supposedly jovial, like the gourmandising Falstaff. Feather- bedded by their own flesh, they embody the resilient spirit of comedy. Thin men belong in tragedy: Yeats once suggested that Hamlet probably ate nothing but flies. But the joke in the name of Leigh's company makes the two identities change places. If the stomach determines temperament, how do we classify the bulimic Nicola in Leigh's Life is Sweet, who so violently belies the film's title? Officially she consumes only cigarettes, which suppress appetite; then at night she binges on toffees, retching cathartically into a plastic bag. During sex, she requires her hapless boyfriend to lap chocolate paste which she smears across her gaunt chest.

Leigh himself balloons towards the waist, but the tummy he so proprietorially caressed is no guarantee of good humour. His face is as doleful as a tragic mask; his eyes are glumly downcast. Hilarity in his work often shrills into hysteria, or sags into depression. Abigail's Party, killingly funny, ends with an abrupt and intolerable death. His new comedy Secrets & Lies begins at a funeral. "You've got to laugh, ain't you, sweetheart?" says Brenda Blethyn, playing a woman traumatically reunited with the daughter she gave away at birth. "Else you'd cry." It's hard to tell whether she is chortling or sobbing.

The protagonist of Secrets & Lies happens to be a fat man whose body does not correspond to what's inside it. He possesses a soul, despite its porky exterior cladding, and at the end, in a moment which is almost a benediction, one of the other characters says to him, "You're lovely." The role is played by Timothy Spall, to whom Leigh paid an interesting tribute in our conversation: "Tim is a caricaturist in the great tradition. I mean that in the organic sense." The organism he was referring to is Spall's body, a byword for gluttony and disgust in their previous work together. In Smelling a Rat, which Leigh directed for the Hampstead Theatre, Spall played a flatulent vermin-exterminator called Vic Maggott, and in Life is Sweet he was a slobbering restaurant owner, who nibbled on his female staff while dishing up trotters coated with marzipan and sparrows swimming in treacle. Leigh himself is a talented cartoonist; Spall is a real-life cartoon, who might have been drawn by Hogarth or Grosz.

The new film makes amends by giving Spall some elegant linen suits to wear and turning him inside out. "It shows Tim the way he really is," said Leigh. "He's a gentle fellow. Of course he's got a great sense of the grotesque. We're both delighted by the dignity of the grotesque. But it doesn't matter what people look like. We're all just ordinary folk." Contradictions clutter these remarks. Obviously the way people look does matter. Leigh's comedy examines what he calls "quips, quiddities, foibles" by fixing on physical mannerisms in which character is encoded: the bossy, swaggering gait of Alison Steadman in Abigail's Party, or the bent, scuttling walk of Blethyn in Secrets & Lies, which looks as if she is apologising to the world for the space she takes up and promising that she'll soon be gone.

"I bet," said Leigh when I questioned him about this, "you could see some funny walks outside this window." His offices are in Soho, in a building shared with a sorority of French models, named on their buzzers as Fifi, Josette and Zaza; perhaps their overflowing bidets account for the damp blotch on Leigh's wall. The passing trade below the window included legless winos, acrobatic couriers, yuppies giving attitude to their cellular phones, and Fifi's furtive, lurking aficionados. But are any of these people "ordinary folk"? Is there any such thing? And when Leigh spoke about "the dignity of the grotesque", had he bitten his tongue to stop himself from using another, less respectful word - indignity?

Leigh has often been accused of despising the characters in his films and deriding their infirmities; he is said to cast a patronising eye on their naff decor and their pretentious vowels. "Nowadays my work is seen in lots of countries, and that complaint is only made here. It's uniquely English. I won't even say British, because I don't get it from Ireland or Scotland. Of course my people are types. But they're not stereotypes. They're too idiosyncratic and individual for that." Again the problems multiply. What difference is there between a type and a stereotype, since both make humbling assumptions about predictability, based on the evidence of physical tics and quirks or verbal catchphrases? And doesn't the art of caricature take a wicked pleasure in denying individuality? An individual is indivisible. Once an actor has perfected someone's walk or twitch or vocal inflection, that person's secret has been stolen. A living creature has become an automaton.

Comedy practises a sinister magic, and although Leigh insists on his own fat, feasting geniality, his work testifies to a battle between the savage glee of laughter and a kinder, more compassionate enjoyment. His films tend to lapse from satire into a fuzzier, more sentimental fade- out. In Life is Sweet and Secrets & Lies, Steadman and Blethyn are the earth mothers who bring about implausible reconciliations; even Johnny, the Mancunian Manichean so frighteningly played by David Thewlis in Naked, is redeemed by the love of a good woman when his former girlfriend dresses his wounds and sings him a lullaby. "Johnny might behave monstrously," Leigh commented, "but he's not a monster or a devil. He's a victim too. The society has failed him. He spends his time lamenting the erosion of its values. I'd blame the education system for letting him down."

That seems to be a disappointingly tame account of this nihilistic jester, but the remark is typical of Leigh, who relies on his characters to tell corrosive truths or to act out scathing revenges on his behalf, while he - like the ventriloquist aghast at the dummy's foul mouth - denies responsibility for their antics. There is no point in asking Leigh to rationalise what he does, or to inspect the mixture of aggression and ingratiation which turns a man into a comedian. His work dramatises these contradictions; it would be less engaging, and also less troubling, if it safely resolved them.

Secrets & Lies may be as close as Leigh - taking cover behind the ample physique of Timothy Spall - has so far come to self-revelation. Spall's character is the owner of a High Street photographic studio, who specialises in weddings. Leigh takes this job very seriously. "Tim and I spent a day doing researching with a photographer just like the one in the film. He was an affable guy, but we could see him getting tense at this wedding. He had to rush back to the studio to develop his rolls during the reception - if they hadn't come out properly, he'd have been in the shit. It's a huge responsibility. People depend on you to make them look the way they want to, at these great rituals in their lives. I wanted to show what tact someone like that needs. A photographer has to be a diplomat, because he's dealing with all kinds of different people all the time, most of them nervous because they're having their picture taken. And Tim's character coaxes his customers to smile, making his little jokes even though he's full of pain."

Leigh calls Secrets & Lies "a film about identity, about how we perceive ourselves and others". He understands the lens's dubious contribution to that process. Marianne Jean-Baptiste, as Blethyn's long-lost daughter (who disconcerts the family by turning out to be black), is an optometrist, seen at work testing spectacles. She corrects and cleanses vision; Spall, as her befuddled uncle, does the opposite. The camera is supposedly incapable of lying; High Street photography studios - with their rusticated backdrops, their diffused light, and their discreet touching-up of blemishes - make sure that it tells us flattering fibs. Leigh has a family connection with Spall's business. His grandfather Mayer Liebermann worked as a portrait miniaturist in Manchester. He didn't take photographs, but tinted and ornately framed those people brought to him, making dim eyes sparkle and imparting the bloom of youth to defunct cheeks. The Second World War was his boom-time: dead sons who now existed only in dog-eared holiday snaps were exhumed by Liebermann's alchemical dabbing, and could be set up as mantelpiece icons.

A benign God - disproving Johnny's claim in Naked that he's "an evil bastard", who created the world in order to fuck it up - invented the High Street photographic studio so we could entertain the illusion that we look better than we actually do. Leigh's grandfather rose-tinted the world. Leigh himself, perhaps repining, after the pessimism of Naked, has done the same in Secrets & Lies. "I try to give each film its own tonality. Naked was a nocturne, it had to have a blue-black look. There were no reds in it at all. The designer Alison Chitty went bonkers if we were shooting in a street where a red car was parked. We had to find the owner and get him to move it, otherwise we couldn't go ahead! For Secrets & Lies we decided to use Fuji film-stock, which lends itself - and I mean this as a compliment - to the palette of High Street photography. It has a less saturated look. This time we allowed ourselves to use red. You'll see lots of blue in it, and even pink."

But Spall's love-affair with soft focus and the merciful filter is only temporary. His last client is a glacially beautiful blonde woman. She poses with the blank disdain of a professional model, then turns her face to one side to expose a scar which snakes from her forehead to her jaw with stitch-marks like barbed wire. This is exactly the kind of stigma which High Street photography exists to finesse. But the woman wears her cicatrice proudly and vengefully. "I want it," she tells Spall, "to look as bad as possible", and she makes him train all his spotlights on it. The pictures are her evidence against the driver of the crashed car in which she was a passenger. The photographer who spends his time eliciting smiles now has to contemplate a wound: the outward sign of the internal damage which most of Leigh's people more covertly carry round with them. (There are long, harrowing close-ups in Secrets & Lies when Blethyn's face seems to cave in, tugged out of shape by the misery and remorse she keeps suppressed beneath the skin.)

The photographer, sorting out his family's imbroglios and evasions, blames the habit of keeping secrets for our hurt and unhappiness. In doing so doesn't he censure Leigh's own creative procedures? Leigh insists, during the improvisations from which his films derive, that the actors know only as much about one another as their characters would; he conspiratorially isolates them, and even requires the production team to take a vow of silence about the plot.

Leigh fumed politely when I pointed this out. "With all due respect, the two things have got nothing to do with each other. My keeping secrets is a technicality - it's a practical matter. Like not letting light onto the film before it's developed: if you do that, it won't come out. And I maintain this principle of the 'need to know' because that's the only way that we can develop the story truthfully. I've got no cult or orthodoxy of secrecy. I don't much care for it, In fact." Yet he went on to confirm my hunch about his ferocious protocols and the paranoia which upholds them. "The security on this film was more rigorous than ever before. The call sheets we handed out each day had a special cover-page attached saying, 'THIS DOCUMENT IS CLASSIFIED'. The crew were kept in the dark too, down to the sparks and the painters. No one was allowed to know who this black woman was when Marianne Jean-Baptiste turned up at the party, except for Brenda Blethyn who's playing her mother. That's the only way we could make sure that people reacted truthfully."

That truth is validated by the confusion or distress of the performers. To me, this sounds more like vivisection than theatrical make-believe, and what makes it slightly sinister is Leigh's supervising omniscience. While researching her part as the nerdy nurse in Abigail's Party Janine Duvitski went to the supermarket in character, and picked out only items which her alter ego would have bought. Then she remembered that she needed food for her own dog. Leigh, who had been creeping down the aisles behind her, suddenly reared above the pyramid of Pedigree Chum and wagged a chastening finger: "Your character doesn't have a dog!" David Thewlis remembers speedily improvising his way into bed with the punk played by Katrin Cartlidge in Naked. Then Leigh arrested their sweatily authentic foreplay, ordering, "Come out of character." Thewlis found it hard to detumesce on command.

"It's all in the course of duty," Leigh said. "The actors have an artistic contract with me. My job is to tell the story. They can't do that, any more than I can act it. I'm allowed to keep moving the parameters they work inside, to stop it getting dramatically meaningless." Once more, he seemed to be agreeing with me, not rebutting my point. "I have the power to stop these improvisations whenever I want. I'm the dramatist! It's terribly strict. There's a rule against the actors imagining they are the characters. After I tell them to come out of character, they must always use the third person when they refer to whoever they're playing. There are actors around - a lot of them - who want to be the character and use the first person in discussing whoever it is. But they don't get on with my method."

That method, clearly, is not the "Method", with its primal screams, mucky recovered memories, and compulsory mumbling. But - and this may be responsible for the extraordinary results, because comedy is a crazed and dangerous business - there is madness in it, and also a certain manipulative cruelty. Michael Coveney, in his recent biography of Leigh, describes his bizarre orchestration of sexual intercourse for a scene in a radio play. The actors took off their clothes and retired to bed in an Islington house; Leigh recorded the ensuing grunts and moans from a van in the street. Since this was radio, wouldn't a few disembodied sound-effects have done just as well? And since the performers had agreed to copulate for real, why should Leigh have called a halt just before penetration, so that the actor - coming out of character in a queasily literal sense - climaxed into a cushion? Leigh, the absent but all-knowing god, was prophylactically present in the bed between them, despite being holed up in his eavesdropping van outside.

Yet a tell-tale vacancy remains in Secrets & Lies. Blethyn does not relinquish her ultimate secret, which is the identity of Jean-Baptiste's black father. She first says she has forgotten, then wails in anguish that the revelation would break her heart. Does the actress know something which she keeps hidden from the director? Leigh could not countenance that possibility. "No, no, she and I have a shared understanding." Then why aren't the rest of us let in on it, at the film's emotional peak? "I would not want," he said, "to devalue or pervert the social currency of the film by calling up racial stereotypes. Do you see what I mean?" The careful stiffness of the jargon, untypical of Leigh, was another warning sign posted against trespassers. Comedy is a way of venting rage or pain, but Leigh is less ready to exhibit his scars than the woman in front of Spall's camera.

Alison Chitty has described the experience of collaborating with Leigh as "solidarity around a black hole". I asked him what it felt like to be one of those mythical cavities in space - a gluttonous emptiness, which can gobble up entire worlds. "Well, she didn't mean me, she meant the way I work. And yes, it is terrifying sometimes. There's always a moment when I think to myself, 'Jesus Christ, I wish I had a script!' No, no, I never think that ... But I did have a bad patch in Secrets & Lies, when I couldn't see where it was going. You just have to keep exploring, until you find a way." Despite these attacks of panic, Leigh maximises the danger. To keep all the options open, he gives his films titles at the last possible moment. "The actual deadline is when the guy has to do the graphics - not before. You don't need a title until it becomes necessary." The title he finally chose for a film which was known throughout production as Untitled 95 revealingly begs some crucial questions, and worries away at the conflict within him between genial comedy and abrasive satire, between the fat man's belly laughter and the thin man's misanthropy.

He acknowledged one half of the problem when talking about the verisimilitude his actors aim for: "I know it's a fiction - though we want to tell the truth." Spall may denounce lies in his final sermon, but without a constant barrage of them, ranging from innocuous white ones to life-saving whoppers, how would we get through the day? Why else do we need art? Leigh's secretiveness is equally perverse, and quite unavailing. When I asked where he shot his current film, the anonymous Untitled 96, he said grudgingly, "In London - but I'll only tell you that because people saw us on location in the streets." Earlier he described the making of Secrets & Lies as "a tiny version of World War II". Could it have been military necessity which dictated the glowering embargoes on disclosure blazoned across the call sheets? Leigh, like the rest of us, is entitled to his privacy; at present - poor man - he is skulking behind his beard, infuriated by tabloid gossip about the break-up of his marriage to Alison Steadman. But though he mystifies his methods and obscures his motives, his work has fewer inhibitions. The more sullenly he guards his secrets, the more candidly his films blurt them out.

! 'Secrets & Lies' (15) opens on Friday.