It must be awful being Ewan McGregor. You have to work with these iconic directors such as Woody Allen.

You get paid for it. And you have to do love scenes with Hayley Atwell.

That name rings few bells at the moment, although the almost ridiculously beautiful face will be familiar if you were one of the millions addicted to The Line of Beauty, this year’s big BBC drama about life and gay times in Thatcher’s Britain. Virtually straight out of drama school and then only 23, Atwell played Catherine Fedden, the psychologically disturbed daughter of a rich Tory politician, the only chink of darkness in an otherwise perfect vision of 1980s affluence and wealth. Other than an advertisement for Pringles and a tiny part in a drama about Charles and Camilla that ended up on the cutting-room floor, it was her first television job. Critics sat up and took notice. She more than equalled Dan Stevens, the other young unknown, who played the central character of Nick Guest and had the lion’s share of publicity in the run-up to the series. The mature assurance of the performance of this west-London girl, coming seemingly from nowhere, was matched by her physical presence. It was what separates a star from merely an excellent actor — you could not take your eyes off her.

Woody Allen presumably agrees. Here we are a year later, and he has cast her as the female lead, alongside McGregor and Colin Farrell, in his as-yet-untitled summer project, which has been filming in London and Brighton.

It is the story of two brothers drawn into a life of crime, and she plays McGregor’s girlfriend.

“It’s wonderful and it’s terrifying,” she says. “Being my first film, and having to just listen, more than anything else, and taking it in, and being clear about what’s needed.

Woody has great faith in English actors. With him it’s a given that he doesn’t have to do line-reading with them. He doesn’t faff around with too many shots. We’ve been improvising quite a lot of the dialogue. I feel very safe with him.”

During the love scene with McGregor, Allen, she says, sat in the corner, eating a tomato sandwich. “As I’ve got to know him, I can’t stop going up to him and want to have contact with him. He’s lovely.” She likes the fact that he is “outside the system”, and that there is not the usual Hollywood obsession with hierarchy. “Everybody gets paid much the same; we get the same manky trailer, the same dodgy catering. There are no airs and graces — we get treated exactly the same.”

Atwell is sitting on a tall stool, being teased and coiffed by a make-up artist before a photo shoot in a deserted part of London’s East End. She takes this whole process in her stride, with an unfussy application that belies her age and relative inexperience. Her features, which in The Line of Beauty had a darkness, even a faint brutality, about them that managed to suggest damaged goods, are much more delicate in the flesh, and besides, she smiles a lot more than Catherine.

We first met a month ago, just as she was preparing for filming, when she told me that the part in the film had, in fact, had little to do with her television debut. “I went to a casting initially knowing that there were hundreds of girls going up for it,” she recalled. “I just read a scene, and I had no idea who she was, what the character was doing, the title of the script, nothing. It was very, very secretive. Two weeks later, I got a call saying, ‘Woody wants to meet you on Monday morning. Will you go over (to New York)?’” It was, she says, a surreal moment, but she talked herself into a feeling of detachment. “I formed no opinions about him or what to expect; all I knew was that I’d probably be there two minutes, stared at up and down and then asked to leave.” She was put up at a hotel she describes as like something out of The Shining, and wandered about New York before turning up at Allen’s office at the allotted time. “He came in and he was more nervous than I was.

He said, ‘You know, I don’t really like doing this.’ I just read for him, he asked me a bit about my personal life, and we engaged — as much small talk as you can have with Woody Allen — and that was it.

“I got back to the hotel with the script, and I read it, and I liked the character, and I thought the script was interesting, and I called up to tell them that, and the assistant said, ‘Well, he might actually tweak a few of the scenes, as he’s now got somebody in mind for the part — oh, sorry, Woody would like to offer it to you.’”

However thrilling all this may be, Atwell attempts at least to keep a clear head about where it will all lead. Barely a year has passed since she left the Guildhall, but in that time, alongside The Line of Beauty, she has appeared in the Royal Shakespeare Company’s production of Women Beware Women and in Prometheus Bound at London’s Sound Theatre, and she has roles in two forthcoming BBC dramas — Fear of Fanny, in which she plays the television chef Fanny Cradock’s assistant, and The Ruby in the Smoke, an adaptation of a Philip Pullman novel, which co-stars Billie Piper. She has also had a brush with the workings of mainstream Hollywood, having been seriously in the running for one of the starring roles in the forthcoming historical drama The Other Boleyn Girl. Scarlett Johansson, being a name, won out in the end. Atwell realised how attached she had become to the role, but accepted that that was the way things worked in Tinseltown. “It’s a dangerous game,” she says. “And I feel like, if it does come, when it comes, it’s something I will handle very delicately.”