And she almost turned down the role of Lady Edith.

She had just been offered the role of Viola in a touring production of Shakespeare's Twelfth Night, and initially thought the role on Downton would be a small one.

"A few days later my agent said, 'You have an audition for a period drama.' I thought it was going to be a 'Yes, milord,' a half-day's filming, one line maybe. But it would be good to have on your CV that you'd done telly. And I thought, 'I'm going to have to turn down this dream Shakespeare for this TV job. What a disaster!' And it was 'Downton.' So I went and read and realized it was for a lead part. And I don't know how it happened," she said.