The face of the bookseller says it all. He’s working behind the counter when Poppy (Sally Hawkins), the kooky, smiley protagonist of Mike Leigh’s new film Happy-Go-Lucky, walks in. It’s the first dialogue scene in the film. “Hellooooo,” she says, beaming. She follows this with a little coquettish “Huhhh.” It’s a giddy inhalation, a comic non-verbal exclamation somewhere between David Brent and Roland Rat.

The bookseller, unimpressed, glowers. “ ’Avin’ a bad day?” she persists, skipping and jittering around the store. “No,” he says, deadpan. “Huhhh, not till I showed up, eh? Huhhh!” comes the reply. His glower becomes venomous. “Look like a rabbit caught in the headlights!” she continues, unfazed, adding, “Huhh! Don’t worry, I won’t bite!” She turns to leave. “ ’Ave a good day! Stay ’appy!” she says, still beaming, still jittering.

The bookseller’s face says it all. “Wow, she’s annoying!” he’s thinking. And, unsurprisingly, so are we. But he’ll never see her again, whereas we’ve got her for an entire movie.

Make no mistake, Poppy is annoying. Her upbeat sugar-rush persona, her zany outfits (leopard-print boots, lime-green tutus and pink bras) and her wacky, unfettered free associations (“Be amazing to fly, wouldn’t it?”) permeate a movie that randomly follows her through driving lessons, flamenco classes and minor emotional disturbances, but is fundamentally a full-bore homage to these same eccentricities. Worse still, she threatens to alienate any prospective audience that is expecting either the bittersweet miserablist poetry of traditional Mike Leigh movies (Vera Drake, Secrets & Lies) or just a protagonist whom you don’t want to slap.

Leigh, typically, is having none of it. The film is expressing something very important, he announced with typical self-effacement at this year’s Berlin Film Festival. “At the beginning of the 21st century, when we’re in a world that’s heading towards disaster, it’s important to reject the growing fashion to be pessimistic and gloomy,” he said, referring to the film’s validation of Poppy’s perky point of view. “Everywhere there are people on the ground getting on with it, and being positive.”

More intriguing, however, is the idea, validated by the Happy-Go-Lucky co-star and Leigh regular Eddie Marsan, that Poppy is actually supposed to be vaguely annoying. “It’s a funny film,” he says. “Because when you first see it, you think that Poppy’s not in the real world; you judge her, and you think, ‘Oh look, she’s just a little hippy.’ It’s a character that can be very irritating if you’re not careful.”

However, Marsan says that after his third viewing of the film he suddenly got it – Poppy’s superhuman optimism and giddy mannerisms are specifically emphasised to force you, the viewer, to question your own attitudes and prejudices, your own dependency on cynicism and negativity. “At that point you realise how much courage it takes to maintain that level of happiness,” he says. “And then, that’s when you start to admire Poppy.”

It’s a nice theory, but it smacks of a counter-intuitive approach to storytelling. Make them hate you just so they can hate themselves and then love you in the end? In the absence of an empathetic central character the movie opens up with gaffs, misfired vignettes and credibility lapses. Here there’s an odd nightclub scene straight out of the 1980s, a bourgeois suburban nightmare scene straight out of Abigail’s Party and a seemingly symbolic nighttime scene with a stuttering tramp straight out of Leigh’s own wildly alternative reality.

Of course, it’s not the done thing to criticise Leigh, who is, alongside Ken Loach, one of the revered godfathers of the British film industry. Indeed Happy-Go-Lucky is being hailed in some quarters and in some parts of the press as the panacea for all our cultural ills. Nonetheless, there has been a small but vocal minority of dissenters who have dogged Leigh throughout his career. When Abigail’s Party was broadcast in 1977, the late dramatist Dennis Potter was incensed, calling the project, “a prolonged jeer, twitching with genuine hatred, about the dreadful suburban tastes of the dreadful lower middle classes”.

As he developed as a director, the Salford-born Leigh, a RADA theatre graduate who frequently clashed with both teachers and theatre bosses (he was always assured of his own genius), became as famed for his creative method as he was for alleged class-based misanthropy. His movies were built from months of rehearsals and improvisations, with scripts born completely from character interaction. Films such as Life Is Sweet and Naked bristled with a memorable vernacular that spoke of the bleak tragedy that dwelt just below the humdrum surface of unseen working-class England. In Naked, for instance, an angry, unemployed David Thewlis announces bitterly, “You can’t make an omelette without cracking a few eggs, and humanity is just the egg – and the omelette stinks.”

The dissenters, naturally, spotted a phoney. The London-born but US-based film critic David Thomson, in particular, wondered “whether something in Leigh dreads the very people he has spent his life listening to”. He called this a “profound conflict” in the work, and questioned whether “Leigh isn’t actually driven forward by a kind of disgust or despair at these people. Is he a true working-class artist, or a middle-class listener appalled but fascinated by the junky speech patterns?”

The awards mounted up (a Palme d’Or for Secrets & Lies, a Venice Film Festival Golden Lion for Vera Drake), yet in interviews Leigh was occasionally forced to defend himself. “Some people say that I caricature working-class people, but sometimes I caricature middle-class people. There are all sorts of things floating around which I think are crap,” he said, responding wearily to the accusation of class snobbery. More recently, after a London Film Festival screening of All or Nothing he simply refused to engage with the criticism, greeting the accusation with the stock response, “I have nothing to say to that.”

Thus Happy-Go-Lucky, may be an attempt to save a 21st-century world that’s heading towards disaster, but it’s also a testament to the old Leigh foibles. Look at the language he uses to defend it: “Everywhere there are people on the ground getting on with it.” The implication here is that Leigh is somewhere above the ground, looking down on his subjects with his godlike prerogative.

In other words, the very thing that Happy-Go-Lucky is supposed to be doing – breaking with Leigh’s movie past, celebrating optimism – is undercut by the director’s own instincts. In doing so, and in creating the character of Poppy, Leigh might have unwittingly made not the best and most pleasing movie of his career, but the worst. Happy-Go-Lucky is out on April 18

Master of the mundane: Mike Leigh’s movies

Abigail’s Party (1977)
A BBC Play for Today and the template for every nightmare evening with the neighbours since it was aired, starring Alison Steadman as the toxic hostess

High Hopes (1988)
A London courier, his partner and a big, prickly cactus called Thatcher

Secrets and Lies (1996)
A family in near meltdown after a series of devastating revelations. But Brenda Blethyn (“Alright, daaaarlin’ ”) wins through

Vera Drake (2004)
Imelda Staunton gives an acclaimed, Oscar-nominated performance as a 1950s abortionist

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