Win an award, don’t work again for a year!” says Kerry Fox cheerfully as she tucks into lunch at a North London pub. “That’s the classic one!” And she roars with laughter.

Fox laughs a lot as she chats about the highs and lows of her 18-year career. This is surprising, given her reputation for being extremely serious about her work; for being, as they say in Hollywood, all about the craft.

It was her eerie intensity that marked her out as a future star in her breakthrough role in Jane Campion’s 1990 film An Angel at my Table – a career move that, typically, was the opposite of glamorous, requiring her to gain two stone and don an orange wig. And throughout her career, the New Zealand-born actress (she has lived in the UK since 1994, but traces of her Kiwi accent remain) has shunned the easy, bread-and-butter roles and sought out projects that offer her a challenge – romping with Sophie Ward on primetime TV (A Village Affair), for example, or demanding roles in such high-profile films as Shallow Grave and Welcome to Sarajevo – if she believed in the intrinsic value of the drama.

Indeed, it was the quest for actorly authenticity that led her, in 2001, to accept a lead role in Patrice Chéreau’s controversial Intimacy, in which she and co-star Mark Rylance shared numerous frank sex scenes, including one that was unsimulated.

Recalled now, if at all, as a piece of arthouse smut, the film started out with impeccably intellectual credentials; it was intended to be an exploration into the limits of physical and emotional closeness rather than an exercise in porn vérité. But, after scooping fistfuls of awards on the festival circuit, the film stoked several hyperventilating newspaper columnists into a moral panic before sinking without trace at the box office, taking Fox’s career, temporarily, with it. “A lot of people wrote about it who hadn’t seen it,” she says. “That really undermined it. And then it was released in America the same week as 9/11, so that was that.”

The furore was stoked when Fox’s partner, the journalist Andrew Linklater, wrote a detailed article in The Guardian about his conflicted reaction to the film. The pair were six months into their relationship when Fox first got the script to read, and while he could intellectualise the necessity for cinema to fulfil its “voyeuristic” purpose, he admitted to feeling both jealous and slightly, guiltily, intrigued. Fox was not at the time particularly overjoyed that Linklater had rushed into print with his views, but the relationship survived; indeed, the release of the film coincided with the birth of their first child, and she found herself in the unusual position of chatting to journalists about fellatio in between bouts of breastfeeding, with the film’s publicists doubling as babysitters in the next-door room.

In retrospect she can allow herself to be philosophical about the effect all this hoo-hah had on her career: “Actors’ careers go up and down in ways you can’t control. But I do look at the men I work with, and there’s no doubt they have more opportunities. As a woman, when you reach a certain point, where can you go? You can be the other woman. Or you can be the mother.”

Her latest role falls into the latter category. Channel 4’s gripping feature-length drama The Shooting of Thomas Hurndall tells the true story of an English photography student who went to Gaza as a peace activist in 2003, and was shot by a sniper while trying to usher a group of terrified Palestinian children to safety. With Thomas in a coma, his parents, played by Fox and Stephen Dillane, take on the Israeli Defence Forces in a legal battle to bring Hurndall’s killer to justice, and become embroiled in the complexities of Middle Eastern politics.

Fox gives a typically well-judged performance. Resisting the temptation to chew the scenery, she plays Jocelyn Hurndall with restraint, quivering with the carefully controlled anguish of a woman who simply can’t afford, yet, to unleash her grief. For such a committed actor, the experience was desperately intense. “I was crying every single day,” she recalls. “I just felt constantly on the edge of despair. But nobody wants to watch that endlessly on screen. It’s not comfortable watching someone being passionately emotional the whole time.”

The day before she flew to Jordan to begin filming, Fox asked for a meeting with the real Jocelyn Hurndall. “I wanted to reassure her that my motives were honest,” she says. “I couldn’t guarantee the outcome but I wanted to tell her that I’d do my best. It was a duty. She’s very . . . beautiful. She struck me as someone who is incredibly engaged with people, very attentive. People like her, who have suffered in that way, sort of carry it on them, in their being. I wanted to say to her that I wouldn’t let her down.”

Like all the characters Fox is drawn to, Jocelyn Hurndall is defined by the suffering that she has survived. “People who’ve been through extraordinary events become incredibly rich and strong, and that’s very appealing to me. They’ve had to assess themselves and where they are in the world, and how they are, and what they have done that’s got them to this point.” But playing them takes its toll, and Fox – visibly tired today – has had to battle against emotional exhaustion in at least two other recent projects. In Bright Star, Jane Campion’s forthcoming film about John Keats, she again plays a distraught mother, Mrs Brawne, whose daughter is in love with the penniless poet.

On Campion, Fox remarks: “Jane just oozes intelligence and interest and astuteness. It’s very enriching for me, but it’s hard and scary as well. My body completely cracked up. I was in a corset all the time and the character was incredibly self-contained, and I became very . . . still. I was playing a woman who was terrified that her daughter was throwing her life away and underneath it all was quite depressed. So I was depressed as well, and I was in agony. I had to be attacked by the osteopath, who had to sort of uncrease me. But acting is a physical thing; you respond physically.”

Some actors talk about performance as therapy; for Fox, despite all the cheerful laughter that punctuates our conversation, the process seems more like trauma. Does she ever worry that she’s doing herself lasting damage by taking it all so seriously? There is a long, silent pause. “I think it’s left its mark on me,” she says slowly. “It’s made me the way I am. But it’s fundamentally good to try and understand how people work. Sometimes people have said that things they have watched have helped them or given them courage, and that’s fantastic. To me that’s great.”

The Shooting of Thomas Hurndall, Mon, C4, 9pm

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