In the film Hampstead, Diane Keaton plays a woman struggling with debts left by her late husband as she befriends Donald (Brendan Gleeson), a homeless man living in a shack nearby. "It's a really good story," Keaton says, "about that certain point in your life when you feel that nothing will ever change for you, that you're stuck forever, that you're older and you don't really have any use in this world. But then you address those issues you didn't want to address and stop being afraid."

Diane with her onscreen son James NortonDiane with her onscreen son James Norton

She feels that these themes helped her sympathise with her character. "I do identify with Emily in a sense of being a coward," Keaton says. "She's kind of a coward in the beginning. She doesn't tell the truth. It's easy for me to identify with her problems because they're the problems that I feel I also have. She's a modified version of me!"

She goes on to explain how she understood why Emily was drawn to Donald: "She's as much a victim of her life as Donald is. She's in trouble too. She's not able to pay her rent, she was betrayed by her husband, she has a difficult time even with her son because he's making her feel inadequate. So meeting Donald opens up a whole new world."

Keaton is famous for her personal sense of style, which she brings to the role. "It's all because of Annie Hall," she laughs, referring to her Oscar-winning character in the Woody Allen classic. "I'm not a glamour person; I'm basically a sports person! But if I'd had an education, I'd have been a designer. My education is basically that I graduated from high school, and from there I went to acting school. Because I think that the performing part came first."

Keaton recently participated in a 45-year reunion with the cast of The Godfather. To prepare for the meeting, she watched the Godfather movies for the first time in 30 years, and says that they're still "great, so powerful and such genius".

Of seeing her friends and colleagues in person after all these years, she says, "It was very moving. But it was also very sad, because a lot of people aren't with us anymore. To me, the other actors are the most important people. It's not about me, it's who I'm acting with, how I respond with them and how we together make something of these characters. To me that's the most fun."

Watch the trailer for Hampstead: