'And at the end he said, 'Do you believe me?' I said I did, and he said, 'It's not true!'' Binoche says, recalling that Kiarostami was tickled by the way she had been captivated by his story. 'I laughed so much. After that we decided to make a movie out of it because the story's so good.'

Having committed themselves to the project - they even fingerprinted a makeshift agreement - Binoche returned to France and found a producer: MK2's filmmaker-turned-svengali Marin Karmitz, who had produced Kiarostami's 2002 film, Ten. And so the director's first feature-length film set outside Iran was born.

The story which so perplexed Binoche four years ago has since been adapted into Certified Copy's narrative backbone. The film begins with British writer James Miller (played by opera singer William Shimell) meeting a French antique-shop owner (Binoche) in Tuscany after the launch of the Italian translation of his book about duplication in art.

Receiving her note requesting a meeting, Miller looks for her the day after. She drives him to a small, picturesque town. The pair are initially uneasy. Miller is mildly nonplussed when she asks him to sign six copies of his book; she is irate over his haughty comments about ordinary, unlearned folk.

The tension boils over as they leave a cafe, where the owner mistakes them for a married couple. Their erstwhile discord suddenly morphs into marital strife, with the pair seemingly transformed into an embittered couple. Their initial English-only exchanges are quickly replaced by swathes of bilingual bitterness.

What makes Certified Copy intriguing is that even by the time the film finishes, the audience is none the wiser about the factors behind the duo's abrupt change of behaviour. Binoche - whose character doesn't even have a name - says she's not sure what to make of the relationship either. And she's still unsure whether Kiarostami's original story is fact, fiction or a mixture of both.

'I think [the characters] are playing out a story, but at the same time they're believing in the story,' she says of Miller and 'She', as her character is named in the credits. 'When you believe, it's hard to tell what's true - because belief makes reality. But, you know, I play the part like a stranger, and then as a married woman. So for me all the realities are true, but it's also all false,' she says.

'This reminds me of a conversation I had with Abbas. He said, when you cry in films, those are not real tears and you're faking it. It's not generated by real hurt. But if you cry without real hurt, will the spectator feel the story? Will they believe in it? It might appear to be a simple technical exercise.'

Binoche's reflection here mirrors the philosophical theme Kiarostami wants to explore in Certified Copy: that is, do originals always have a higher cultural, aesthetic or emotional value than replicas? Do an actor's feigned, on-camera emotions have less effect because they are not real responses to a genuine, real-life event? Does a story - like the one Kiarostami told Binoche in Tehran - become less powerful or engaging simply because the original tale has been furnished with invented details, or even totally made up altogether?

Kiarostami probably thinks otherwise, as the film repeatedly suggests the pursuit of authenticity is often overrated. In a discussion about Andy Warhol's Coca-Cola bottle paintings, Miller says it's not the actual object but the re-representation and perception of them that matter. One telling scene in Certified Copy shows the two characters visiting a museum, where a facsimile (albeit a 200-year-old one) of a piece of ancient Roman art has been put on show and treated as a genuine work of art in itself.

This mirrors what Miller says in the film's first scene about the idea behind his book: that is, forget the original, and just get a (certified) copy instead.

It's interesting to know that the dialogue in Certified Copy was originally written by Kiarostami in Farsi. It was later translated into English and French. 'When I wrote it, I didn't have a language for it in mind,' says the director. 'Once it was written, I let my translator carefully turn it into different languages. The only thing which concerned me was at which moment they switched from one language to another [within the narrative]. My films have been travelling in different countries for 30 years, and they have subtitles. So this concern and worry about whether people understand me disappeared long ago,' he says.

Certified Copy is in fact a copy in more ways than one. While it's a reinvention of Kiarostami's own personal experience, it's also a re-imagining of certain films from the past, such as Alain Resnais' Last Year at Marienbad and Richard Linklater's Before Sunrise. And then there's Roberto Rossellini's Journey to Italy, with which Certified Copy shares a canny resemblance. In that 1951 film, a couple (played by Ingrid Bergman and George Sanders) slowly watch their marriage ebbing, flowing and disintegrating as they travel through Italy.

More than just paying homage to other people's work, however, Certified Copy also sees Kiarostami revisiting his own oeuvre as well, most notably in the way he mixes reality with illusion. While a fictional feature film, Certified Copy contains quite a few depictions of real life - the Italian locations, the relic in the museum - in a story driven by artifice and pretence.

This confluence of the real and the fake is a trademark of the Iranian director's past films. In documentaries such as Homework and ABC Africa, he is seen or heard off-screen asking questions. Close Up, a docudrama, is a re-enactment of an identity fraud, with the culprit and victims playing themselves. The feature film And Life Goes On... has a filmmaker and his son travelling through the ruins of a real earthquake, and Through the Olive Trees revolves around an actor trying to woo, in real life, his on-screen paramour - with a filmmaker documenting his travails.

Although Kiarostami accepts the crossover between fiction and reality in storytelling, he is sceptical about the sway or moral integrity an artist wields. In a style that approaches self-critique, his characters - who we can understand as avatars of himself - always come across as mildly cynical. They lack empathy towards the downtrodden and have no idea about social decorum.

In And Life Goes On... the director character doesn't seem to care that much about the many tragic stories he hears from the earthquake victims, while The Wind Will Carry Us revolves around a manipulative television producer who lies about his real reason for being in a village: he's actually waiting for a centenarian to die so that he can score a big scoop for his programme. He even pesters the local residents to go out of their way to meet his needs while he's doing it.

Certified Copy's James Miller is a similar character. He's arrogant, he appears late at his book launch, and even takes a phone call during his own speech. These are probably copies of Kiarostami himself, with the flaws magnified to highlight how art can try, and perhaps fail, to change the world.

Or perhaps it's an artistic game to test the blurry boundary between fact and fiction - an act which has caught Binoche by surprise, and perhaps audiences worldwide too.

Certified Copy opens on Thursday