She said: "I love Sienna, I think she's a wonderful actress, but we've been like two passing ships in the night recently. "I think that's lovely but also sad about acting. You get incredibly close to people and as soon as it's over you don't see each other. "I don't think I'm very good at figuring out female friendships. I think they're quite tricky to navigate."

The 23-year-old star also said she discusses her sex life with her mother, playwright Sharman Macdonald.

She added to Britain's Glamour magazine: "Mum and I would always talk about sex. She'd come up to my room, have me roll her cigarettes and then tell me I'd have to have one with her. "It's not the typical mother-daughter thing but we're extremely close." Mum's a bit mental in a good way.

She's this chilled-out hippy mother. My house was always the one where my brother and his mates would be drinking when they shouldn't be."