The male star of British director Michael Winterbottom's sexually explicit new film has defended the movie, Nine Songs, at Cannes.
Michael Winterbottom said it was a reaction to "prudish" films
Kieran O'Brien, who stars with US actress Margo Stilley, said: "There is no film like this, it is so graphic.
"If people ask 'why make this film?' I would say 'why not?'," the actor said.
O'Brien has been talking about the film at the festival, but Stilley is not publicising her role - and is not named in the film's closing credits.
The film, which includes real sex scenes, has been shown in at the festival.
"People who have seen it, even though they are forewarned about how explicit it is, come out of the cinema saying they can't believe that it's so explicit," O'Brien said.
"People who say they find it offensive are liars. If they say they find it shocking, I don't believe them," the 31-year-old actor said.
The British Board of Film Classification (BBFC) said the film would not be subject to special criteria.
"We don't normally allow depictions of unsimulated sex in an 18 film, unless they can be exceptionally justified by the context of he film," Craig Lapper, the board's chief assistant in charge of policy told BBC News Online.
"It shouldn't just be for audience stimulation," he said. The film has not yet been seen by the board and they could not comment specifically on Nine Songs.
Rock group Primal Scream feature in the film
The Film Distributors' Association told BBC News Online the film did not yet have a distributor in the UK.
O'Brien had previously appeared in Winterbottom's film about the Manchester music scene, 24 Hour Party People, as well as ITV's criminal psychologist drama Cracker.
"Michael only does extraordinary stuff," he said. "What he wanted to do was explore an intimate relationship and tell it predominantly through love-making," the actor said.
"It's fortunate that I know him so we have that trust and I didn't question why he wanted me to do a scene.
"Pretty much everything Michael wrote, we did. The general consensus of opinion was to push it as far as we could."
The film is based around the relationship between two young people, Matt and Lisa.
The scenes are intercut with performances by nine bands the couple go to see, which include Primal Scream, Franz Ferdinand and Super Furry Animals.
Winterbottom put out adverts searching for an actress who would take part in the film but Stilley was an unknown found by Winterbottom's casting director.
'Ordinary and natural'
O'Brien said of his co-star that he "didn't fancy her" - but very protective of her on set.
"On set she was the only woman with a crew of four lads. I know how difficult it was for her.
"To me they were just scenes we were shooting, to be honest, and I was surprised how ordinary and how natural it was," O'Brien said.
Winterbottom has described the film as a reaction to "prudish" films being made at the moment.