We’re in a cinema foyer and Helena Bonham Carter is being photographed. She asks if I’d mind getting her iPhone out of her handbag so she can take a picture. Aren’t there laws against rummaging through celebrities’ bags nowadays? ‘Oh, I don’t mind!’ Her tone is no-fuss breezy, the accent period-drama posh.

Ten minutes later, upstairs in the lounge, the 46-year-old (I had to double-check: she looks half that) is ploughing through a Wagamama takeaway. The bombshell curls are piled into a bird’s nest and she’s kicked off her heels. We’re in London, five minutes down the road from where she lives with her sweetheart of 11 years, director Tim Burton, and their two children. They’ve made seven films together, him directing, her acting, though she isn’t exactly a muse (she’s too loud to be a muse, she says). Now, after playing witch Bellatrix Lestrange, the most unhinged of the scary baddies in the Harry Potter films, she’s a pin-up for a generation of teenage goth-girls. It’s something she loves. ‘Am I a good example?’ The idea cracks her up, but she adds thoughtfully, ‘Well, at least I’m not too thin. I eat.’

Bonham Carter is most definitely having her moment. She was made a Commander of the British Empire earlier this year, and earned an Oscar nomination for her roll as Queen Elizabeth in The King’s Speech. And of course, there’s Harry Potter. On set she shared Daniel Radcliffe’s make-up team, while Radcliffe interviewed her recently for an American magazine – although it ended with Bonham Carter giving him a gentle talking-to about his typecast fears.

Acting young is something she can relate to. Barely out of her teens when she starred in A Room with a View in the mid-’80s, she was pigeonholed as an English rose. In her twenties she found fame ‘overwhelming’. ‘I’m a late developer,’ she says. ‘I only moved out of home when I was 30.’ What took her so long? ‘I think it was Dad’s illness.’

After a ‘happy childhood’, she was 13 when her dad had a stroke that left him in a wheelchair. ‘By staying, I was trying to make things better. Keeping mum going; keeping them both going.’ Her dad died in 2004.

Now Bonham Carter has her own kids: Billy, eight and Nell, four. She whips out her phone again (it’s in a bonkers pink rubber case with giant bunny ears) to show me pictures. ‘I have an unlikely photo of Tim brushing his son’s hair.’ She should sell it to the newspapers (the tabloids love portraying the couple as a pair of hairbrush-dodgers). ‘I could, couldn’t I? “Tim Burton, with an actual comb.”’

She loves dressing up. The chance to slip into the most famous frock in literature – the decaying wedding dress of jilted bride Miss Havisham – is a big reason she agreed to star in a new film of Charles Dickens’s Great Expectations, directed by Mike Newell. Wasn’t she miffed, being asked to play the mad old battle-axe? And her a mere slip of 46. ‘At the start, I was like: Huh. Already? But Mike kept on saying, “You’re the right age!”’

Miss Havisham – hiding away in the dark, plotting revenge on men from the cobwebby shadows of her stately pile – is the kind of role she was born to play. Did she bring her own ideas about the costume? Naturally. ‘I went overboard! I had this idea that her veil would grow over the years, like her grief. It’s a bit pathological. Everything’s a bit overgrown.’  After leaving here, Bonham Carter is off to pick up her daughter from school. She met her partner Tim Burton on the set of Planet of the Apes in 2001. In their first conversation ever (‘small talk, which he frankly isn’t very good at’), he told her that Hampstead was the only place he’d ever felt he belonged.

Eighteen months later, when they got together, he bought the house next door – ‘He wouldn’t have fitted into mine.’ Ever since the pair have famously lived side by side, each in their own house (sounds perfect). But at the moment they’ve got the builders in and are all under one roof. How’s it going? ‘Surprisingly okay.’ Like a holiday? ‘Yes! There’s a lot to be said for being in shouting distance. And it’s cosy. The kids love it.’

Burton is boss on set. At home it’s vice-versa. ‘I’ve always done the cooking, which I love,’ she says. ‘He can warm up. He does his two-minute rice. And gets the drinks ready. He makes smoothies at the weekends. Our daughter once said to him: “Dadda, why don’t you make smoothies instead of movies?”’ And with that she collapses into her biggest fit of giggles yet.
Great Expectations is released in the UAE on Thursday December 13.