There are certain things you expect from a young British actress who has stepped from drama school straight onto a Hollywood movie set – especially if she’s a traffic-stopping brunette with diamond-slicing cheekbones. She’ll be pleasant, she'll be slightly vague, she’ll talk about the craft and she won’t get any jokes.

What you don’t expect, if she’s playing Anne Boleyn, is a detailed analysis of the geopolitical situation in 16th-century Europe, with quotes such as: “The Reformation is difficult to explain to modern audiences. It was a social and religious revolution where faith and politics were synonymous.

Anne Boleyn was like a communist marrying the president of the United States. Henry thought he was the supreme embodiment of God on earth. Why should he answer to the Pope? And how do you argue with people who say, ‘This is God’s will’ – whether that is Henry VIII or an Islamic terrorist?”

Natalie Dormer pauses after she says this, and smiles slightly. “We don’t show as much of that as I’d personally like. And there is lots of sex and violence in the programme, so it’s especially hard to explain it to the guy on the street who’s saying, ‘The Tudors? Tits, man!’”

Although a nit-picking historian might quibble with some of the script decisions in this sex-and-blood-and-frocks-and-gold version of Henry and Anne’s courtship – technically, Henry had two sisters, not one, for instance, and there is no actual evidence that Thomas Tallis was bisexual – Dormer’s performance as Boleyn has cemented her reputation as something of a scene-stealer.

Henry is played by Jonathan Rhys Meyers, and Sam Neill turns in a square-jawed Cardinal Wolsey, but it is Dormer’s blend of innocence and sensuality that has charmed the critics (and that guy in the street), for reasons that will become obvious when the series starts on BBC2 next month. And she has lifted the limelight before. Her bit part in Lasse Hallstrom’s Casanova, as the winsome Victoria, was rewritten by Tom Stoppard to take advantage of her comedy chops. Indeed, her impressive burlesque performance so beguiled Hollywood that she secured a three-picture deal with Disney – placing her in the Keira Knightley league at 23 years old.

“Victoria started off with lots of pouting lips and seductive looks,” she says, toying with a glass of champagne in a north London restaurant. “But they shot the whole film in Venice, and my first day onset was so hot, I was straddling a fan with five layers of petticoats aroundmy waist, in front of 20 Italian crew. So I said, ‘Let’s cut through the crap and have a bit of fun.’”

Of course, following Casanova with The Tudors has its own problems. “I’m tainted by the corset – Helena Bonham Carteritis.” She gives a sly grin. “Now all I want to do is a Shane Meadows film. Please put me in jeans with a fag and no make-up – and please make my call not 5.30am. Anne Boleyn is beautiful, but then she’s been in hair and make-up for an hour and a half.”

Perhaps her wry self-deprecation comes from a last-minute switch to acting from academia. She grew up in Reading, enjoying a “typical middle-class background that everyone with any bohemian values spends years trying to shake off”. She was all set to stride the halls of a history department when she flitted to London with a boyfriend to audition for drama schools.

“I danced from the age of three, I was always in amateur dramatics and I did a lot of public speaking,” she says. “So when I told my family I was going to be an actress ... well, it was like when your camp best friend tells you he’s gay and you’re trying really hard to look surprised. Even so, it was one of the worst years of my life. I was an usher at The Lion King, I was an office temp – the epitome of spiritual bankruptcy – and even a cocktail waitress ... sorry, a mixologist. I can still free-pour a double vodka.”

The academic mind remains sharp, however, as witnessed by her dissertation on Tudor politics and an entirely unprecedented level of preparation for our interview. Unlike any performer your correspondent has badgered, Dormer had gone online before the meeting and flicked through my articles. She then cheerfully quoted my own words back to me. It reduced this questioner to stunned silence, and hopefully it won’t catch on.

Then again, thrust, parry and destruction of an opponent are essentially her leisure pursuits. Dormer fences. “I’ve got dance training and a slightly violent streak,” she explains, “so it’s very cathartic. I’d love to do an action movie, throwing myself from cars.”

With the second series of The Tudors now shooting in Dublin (the show’s debut in theUSA won Showtime its highest ratings for years, while four Emmy nominations nailed the recommission), her greatest regret is the absence of her poker buddies. “I’m missing the circuit out here, so I’ve got all my cronies on a plane in two weeks’ time,” she says. “I started playing in the sixth form. There were five boys to every girl, so it was, ‘Welcome to a man’s world’.” She pauses, realising how that may sound. “Not that sort of poker. I kept my clothes on.”

Yet another thing you don’t expect from a young British actress on the rise.

The Tudors starts on BBC2 at 9pm on Oct 5

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