From psychopath in 'Cracker' to grumpy single mum in the new British thriller 'Downtime': Susan Lynch's roles are getting more sympathetic by the day (which isn't saying much). But then, with bolshy Irish-Italian genes and a childhood spent up a mountain, what else do you expect?

SUSAN LYNCH has played her fair share of psychos. She was memorable in Cracker as one half of a pair of spree killers; played a gangland villainess in ITV's A Dangerous Lady; and even such benign roles as the beautiful Jewess Rebecca in Ivanhoe and Caroline of Brunswick in A Royal Scandal (where she played Princess of Wales to Rupert Everett's Prince Regent) showed a hint of steel behind the classic looks. It's something to do with those formidable dark brows and full lips forever threatening to curl into a snarl: Helena Bonham Carter meets care in the community.

In person, though, Lynch is delightfully laid-back; even when faced with a particularly rude question (we'll come to that later), she's more likely to giggle than take offence. This is a relief, as Chrissie, in the new film Downtime, is another spectacularly surly role for Lynch. A single mum in a depressing Newcastle high-rise, Chrissie spends most of the film bitterly repulsing the advances of Paul McGann as Rob, the weedy ex-policeman who coaxes her down from a 21st floor suicide attempt, then falls in love with her. Romance eventually has its way in the unlikely confines of the lift shaft after they become trapped by vandals. Useless Rob says things like "I'll hold your cardy" while Chrissie hauls herself hand over hand up the cable.

Lynch did many of her own stunts. "On my first day of filming I had to hang 200 feet up [for the suicide attempt]. We thought it would be really amazing for the opening shot of the film, where I actually slip, if you could see the people below me; a close up of my face where you also see the drop. So I said I'd do it. You think, I'll be fine, I'll be fine and when you get there it's OH MY GOD! You know there's these big, hefty men with harnesses and everything, there's no way you're going to fall, but your head's like: I am going to die..."

Lynch is not a mother herself, but some of the most touching scenes involved Chrissie and her young son Jake, played by newcomer (well, at five he could hardly be anything else) Adam Johnstone. "Most of the action scenes we were only about 10 feet up and Adam was harnessed, but he'd stop and say, 'Susan, what are you doing? You're gonna fall!' It took us ages to get the scene because Adam was getting so frightened that I was actually going to jump off. I said, 'I'm acting, Adam.' 'Noooo, I don't care!' But he's the most amazing wee man. And he was a great help with the accent - I was so lucky, having a child with the strongest Newcastle accent you could possibly find."

That disdainful Lynch lip curls a lot in the film, particularly when Rob's around. She found McGann "A lovely man. His soul's near his eyes - he's got the most amazing eyes - so it was quite easy to play someone who doesn't want to go in there until the very end. He has this stare which is just perfect, you know?"

The dashing looks originate from her Italian mother, who met her Irish father in Coventry in the Fifties. "My dad was a busman there and they met at a dance called La Bamba. He fell madly in love. My dad's a real joker, and my mum's just the most alive person you'll ever meet. I was doing a play at the Bush theatre once and [artistic director] Dominic Dromgoole was standing at the top of the stairs when my mum arrived in a cab. The play had already started, and she had no English money. She came running up the stairs of the Bush going: 'I need money for this cab! I'm Susan's mummy!' He said to me later, 'You don't meet your mum. She happens to you.'"

Lynch grew up in Ireland with her four siblings "up a mountain, in complete isolation. We've always been into the idea of making our own humour and entertainment because we didn't have electricity for a time, so there was no telly. Then we got a generator but it kept conking out. John used to run out in the middle of the night with a torch to try and get it started so we could finish watching the film. It was very much us making our own crack, really."

"John" is the actor John Lynch, her brother. Here comes the rude question: Is he older or younger? There's a shocked hiss, then a good-tempered giggle: "He's 10 years older than me! He's my big, big brother, like!" (She's 25). Two actors in one family? "Loads of people ask, where's it come from? And I think it's a mixture of living so far from other people, being all together in the house, and my mum and dad's different personalities. We were always dressing up and acting out whodunnits. We'd play Dallas. Really sad, sad things that if I tell our John or Jackie I've told you, they'll kill me. My sister Pauline still does amateur stuff. She's been an extra in two of the jobs I've done."

A visit, two years ago, to the village just outside Rome where her mother was born made a lot of things fall into place for Lynch. "The atmosphere in our house was never completely Irish, there was always something a bit skew-whiff and as a child you think, what is that? Then when I went there, so many things made sense. Mama's village is just about the basics in life, but how beautiful they are. I remember, we were all sitting at the table, tia Maria brought the food and uncle Pedro started singing to her because she'd made good pasta. Loads of things started to click." All the same, two lots of cultural baggage, two very strong identities... "Frighteningly so! Trying to pull the wool over anyone's eyes in our house is impossible. It makes for a really nice crack, though."

'Downtime' is now on general release