On cringey clothes
'Everything I wore when I was younger was a bit cringe. I had puppy fat and wore unflattering boob tubes, combats and stretchy orange flares. I wanted grown up style even when I was little. Playing Audrey in the school production of Little Shop of Horrors was brilliant because I got to wear leopard print.'
On chic hand-me-downs
'My Mum passed down to me her old Levi's denim jacket. When I left it on a plane, I was devastated. I've never been able to find anything with quite the same cool, faded look.'
On splashing out
'I treated myself to a £700 Chloe bag after one of my very first acting jobs. Then my friends pointed out that, for the same money, I could buy a flight to India. So I took it back.'
On red carpet style
'I never knew until my first film premiere [Fast Girls in 2012] that actresses borrow clothes from designers for the red carpet. Being lent an amazing dress is like putting on a mask - you feel buttressed and protected by it. I loved the dark blue Marni dress I wore at Cannes. It had a studded collar so it felt a bit rock-chick.'
On Downton costumes
'It took me a while to warm to the costumes on Downton. I love it when women accentuate their curves, and that era was all about hiding them. The shapes they wore then were in tune with female empowerment. Cutting off their hair and hiding their busts was a way of saying "we're equal to men."'
On dealing with the paps
'I've only started being photographed by the paparazzi recently. Worrying about how camera-ready you look every time you walk out of the door is a slippery slope. Though my agent did say, "you need to dress a little better now!" [laughs]'
On great Cate
'Cate Blanchett was awesome to work with on Cinderella. When we were filming one of the last shots, she was standing off camera in this bright red coat and was so gorgeous I was looking more at Cate than the set!'
On being understated
'I'd always rather be the girl at the party who's underdressed instead of overdressed. I think it's because I'm tall. If you're petite you can get away with a more dolled-up look.'
Downton Abbey is on ITV now and Cinderella will be released next year
By Lucy Pavia / @lucypavia