Kristin Scott Thomas: The English ice-maiden becomes a queen bitch

It's not often that an actress really gets to shock. But Kristin Scott Thomas manages it in Only God Forgives. A brutally violent Thai crime thriller from Nicolas Winding Refn, if the draw was the Danish director's promised reunion with his Drive star Ryan Gosling, it's Scott Thomas who hijacks the show. She plays Gosling's bitchy bottle-blonde mother Crystal, a “terrifying mafia godmother”, in Refn's words, who smokes, swears and snarls her way across the screen when she arrives in Bangkok.

Not since Shelley Winters's “Ma” Barker in Roger Corman's Bloody Mama has there been such a menacing matriarch – with the oh-so-demure Scott Thomas dipping her performance in pure bile. “I was aware of the character being particularly nasty, and it's the sort of character when I think about her and what I had to do to be her, it fills me with shame,” she says, her pink frock and matching lipstick somewhat shaded by her blushes. “So, yeah, I think it's pretty horrid. I feel slightly grubby having done it.”

Given Scott Thomas has built a career on playing frightfully well-bred women – A Handful of Dust, Four Weddings and a Funeral, Gosford Park – it's unsurprising she found it difficult to flick her “bitch switch”, as Refn gleefully calls it. He and Gosling egged her on. “I'm thinking of one scene in particular where Ryan was particularly helpful with some of the language; things that I never knew existed,” she says, referring to a jaw-dropping moment where she calls a Thai girl a “cum dumpster”.

Far removed from the starchy upper-class roles she's usually saddled with over here, Only God Forgives is entirely in keeping with her recent edgy work in France – from playing a wife who abandons her family for a torrid affair in Leaving to a woman coping with life after prison in I've Loved You So Long. What's given her this brave streak? “I don't know whether it's bravery,” she says, green eyes flickering. “I think 'adventurous' is a better word.”

Certainly, yearning for adventure has coincided with her 2005 divorce from her husband of 17 years, fertility specialist Dr François Olivennes, with whom she has three children. Having remained in Paris, where she has lived for three decades, Scott Thomas, 53, is working harder than ever, although she blames that on acting in two languages. A week after Only God Forgives comes her latest French film, Looking For Hortense. Directed by Pascal Bonitzer, with whom she made 2003's Small Cuts, she's back in her comfort zone here – playing Iva, a theatre director whose marriage to Jean-Pierre Bacri's lecturer is on the slide. “Something like this comes much more naturally,” she says “because it's a little world that I know well – the thinking classes. Not people who are going to whip out guns or slice your throat open – I don't know those people.”

Born in Cornwall, raised in Dorset and educated at Cheltenham Ladies College, Scott Thomas was never likely to be hanging round with thugs and villains. But that's not to say her early life wasn't beset by tears and tragedy. When she was just five, her father, a Fleet Air Arm pilot, died in a plane crash. Six years later, after her mother married another pilot, the family unbelievably suffered the same fate again, when Scott Thomas's stepfather died in similar circumstances. Not long after, she was packed off to Cheltenham, which was a miserable experience for her.

While acting was a dream she'd harboured since she was a little girl, it was when she left London for Paris – initially to work as an au pair – that it became a reality. Joining a drama school, she began to work in theatre, before being offered a role in Under the Cherry Moon, the lavish 1986 vanity project for musician Prince. Bizarre as it was, she embraced it. “I got swept up in this idea that if you have a career, you could be a star,” she says. She trotted off to LA, only to return after three months, reality firmly checked. “Europe is far less competitive than Los Angeles. And I'm terrified of competition. It's something that makes me feel quite sick.” It took years before she'd return – on Mission: Impossible, The Horse Whisperer and Random Hearts.

She has always had an odd relationship with Hollywood. Even her time at the Oscars, nominated for Best Actress for The English Patient, left her conflicted. “To begin with, I was really excited and flattered, and then I realised that I got really sick of it.” The politics of campaigning for an award and “being bombarded with people wanting me to wear their clothes” got to her. Coincidentally, Scott Thomas has just been directed by her English Patient co-star Ralph Fiennes, in The Invisible Woman, which will be unveiled at the Toronto Film Festival next month. The story of Charles Dickens's secret mistress “Nelly” Ternan, Scott Thomas plays her “evil, scheming mother” Catherine.

“I do a lot of evil nowadays! I do evil mothers,” she laughs. She might have gone a little overboard. “The only thing Ralph ever said to me was, 'Kristin, just stop acting!' I was a bit upset about that.”

'Only God Forgives' is out now;'Looking for Hortense' is out on 9 August