Swinton: 'It's a horror film, a love story, a war film, not social comment'

A best-selling novel unnervingly brought to life by the British film-maker Lynne Ramsay has so far been the competition highlight of the Cannes Film Festival. Based on the 2003 book by Lionel Shriver, We Need to Talk About Kevin stars Tilda Swinton and is directed by Glasgow-born Ramsay, who made her feature debut in Cannes in 1999 with the acclaimed Ratcatcher and whose last film was Morvern Callar in 2002.

Shriver's novel is about the mother of a troubled teenage boy who slaughters his schoolmates, and was partly inspired by the spate of high-school killings in the US, most famously the Columbine massacre of 1999. That event also inspired Gus Van Sant's film Elephant, the Palme d'Or winner in 2002, and sparked Michael Moore's gun control documentary Bowling for Columbine.

Ramsay's Kevin is a highly imagistic take on the book, but the film, she says, "wasn't about high-school killing for me. Elephant did that really well, but this film is about the relationship between a mother and son."

Yesterday I interviewed Ramsay and Swinton on stage in Cannes, where Ramsay called the film "a perverse love story, like Greek tragedy".

Swinton added: "It's a horror film, a love story, a war film – it's not social commentary." Herself the mother of twins, Swinton said: "I'm happy to say it's no documentary. I was in the fortunate position, the second I had my children, of being really into them. But I'm aware there are millions of women for whom that never kicks in – and that's a taboo subject."

Ramsay says she was influenced by Roman Polanski, and regards Kevin as "like the real Rosemary's Baby, only not supernatural". She says she could relate to the film's theme from her own family background. "I've seen my own mother with a problematic child – my brother was a difficult teenager, getting in a lot of trouble. She always loved him, although he was difficult to like sometimes."

Kevin marks a welcome return for Ramsay, who has been absent from our screens for nearly a decade: the film industry review Variety said Ramsay was "back with a vengeance".

Ramsay worked on the film for four years, and before that spent five years preparing an abortive adaptation of Alice Sebold's bestseller The Lovely Bones.

Making Kevin was a very different experience, she said: "It's a hiding to nothing if you do a literal translation – I don't have respect for the text like it was the Bible. That happened with The Lovely Bones – [people said] 'Don't change the book we know and love'."

In the event, The Lovely Bones was filmed by the Lord of the Rings director Peter Jackson, but the result didn't impress critics or audiences – or Ramsay. "I don't think the film works," she says. "Sorry Peter, but I think it looks like My Little Pony in heaven."