From Downton Abbey to Daphne du Maurier: Jessica Brown Findlay on playing the spirited heroine of Jamaica Inn

It takes a certain type of actress, weighed down in an ankle-length 1820s dress, to wade out into the rolling surf at Newquay in Cornwall, even with a lifeguard keeping a watchful eye. “The sea is an unpredictable beast,” agrees Jessica Brown Findlay, Downton Abbey’s late Lady Sybil Crawley. “I did go under once and couldn’t see where up is. It’s so exhilarating though – you wouldn’t get that level of fear if you were filming it in a tank in a studio. It’s always good to be a little bit afraid.”

It’s a philosophy that has served the 24-year-old well since her deathbed scene in Downton. “When I left I had no idea what would be in store, if anything,” she says. And if some Downton-esque typecasting followed when she played a reincarnated heiress romanced by Colin Farrell in the romance A New York Winter’s Tale then the BBC’s new adaptation of Daphne du Maurier’s Jamaica Inn– sea-plunging and all – provides a wonderful showcase for talents hitherto constrained by Downton’s corsets.

Brown Findlay is rarely off screen as Du Maurier’s newly orphaned heroine, Mary Yellan, who is sent to live with her Aunt Patience (played by Joanne Whalley) is a remote inn on Bodmin Moor. Much to the morally upright Mary’s disgust, Patience’s husband, Joss (a typically intense Sean Harris), leads a band of smugglers who prey on shipwrecks. And much to her dismay, she also finds herself falling in love with Joss’s roguish brother Jem (Matthew McNulty). “It’s a perfect fusion of gothic romance and a young woman’s rite of passage in the vein of Twilight and Wuthering Heights”, says Emma Frost, who has adapted Du Maurier’s 1936 novel.

Her three-part version puts Mary Yellan squarely back in the centre of the story, and rescues the novel from memories of Alfred Hitchcock’s 1939 screen travesty. “It’s the only time you can remake something Hitchcock did and people don’t throw bricks at you,” says Frost. “Hitchcock’s ended up getting hijacked by Charles Laughton who wanted the character he’s playing, the squire, to become the centre of the film. Daphne du Maurier hated it.”

Frost, who imbibed the local atmosphere by staying in a yurt on Bodmin Moor, has the blessing of the Du Maurier estate, visiting Daphne’s son, Kit Browning at Foy, the house where his mother lived and wrote. “He told me how his mother had been reading Treasure Island and wanted to write a really big epic adventure but to give it a girl as a central character.”

Brown Findlay spends much of the time in mud-caked clothes and rain-drenched hair – a make-under that emphasises her natural pallor and solidity. She’s almost perfectly Pre-Raphaelite. “We decided with the hair that I’d wash it in the morning and then we’d leave it to dry naturally because I’ve got a curl to my hair,” she says. “We just kept everything incredibly minimal so if you are cold you have a bright red nose and blotched cheeks and that’s fantastic because it looked how it would – there was no glamour to this life. It was incredibly refreshing…. I don’t know how many people who like that but I loved it.”

Unlike the 1983 TV adaptation starring Jane Seymour and Trevor Eve as Mary and Jem, which was shot entirely on locations near Padstow, this production was split between Cornwall, Yorkshire and Cumbria (part of the funding coming from Screen Yorkshire), the inn itself being in remote countryside outside Kirkby Lonsdale. Several of Du Maurier’s stories – from Rebecca to Don’t Look Now and The Birds – have been successfully turned into movies, but Frost feels that as a novelist Du Maurier is badly underrated. “As a writer she’s incredibly literary,” says Frost. “People mistakenly relegate her to being a romantic novelist, and yet her view of romantic relationships is really rather bleak.

“I’ve always wanted to adapt Rebecca – and came quite close at one point – so when Jamaica Inn came up I was going to kill to adapt it. I just feel that my voice as a writer is compatible with Daphne du Maurier’s voice… we have obsessions with the same themes. Du Maurier always comes back to gender battles and gender roles, and she very famously said that she conceived of herself as half male and half female. She struggled enormously with her own sexuality and Mary in the book says she’d rather be a boy and she doesn’t want to love like a woman.”

Brown Findlay embodies this splendidly – incidentally showing an impressive prowess as a horsewoman for someone not raised in the saddle. In fact, she was a promising ballerina who by her final year at school was an associate of the Royal Ballet and had danced on stage with the Kirov. Ankle problems put paid to that ambition, but her physical dexterity will be on display in next year’s movie Frankenstein, in which she plays a trapeze artist who falls in with Baron Frankenstein (James McAvoy) and assistant Igor (Daniel Radcliffe). “I trained for the trapeze for three and a half months,” she says. “What an amazing, mad skill to learn.”

Other new ventures include playing Rachel, the publican’s daughter in Posh, Laura Wade’s screen adaptation of her own Royal Court play about a fictionalised version of Oxford University’s Bullingdon Club, and supporting roles in two American movies – Lullaby (with Amy Adams) and Shoplifters of the World, about an obsessive, gun-toting fan of The Smiths.

She seems to be fully justifying her decision to leave Downton Abbey in 2012. “I just didn’t want to do more,” she says. “I was very intrigued to do something new outside of that world.” And as Jamaica Inn’s producer, David Thomson, says: “Jess has an incredible emotional range… she’s a heroine who’s across the screen for three hours” – a fact of which Brown Findlay is modestly aware. “I’m barely off screen,” she says. “When I was watching this I was thinking ‘Oh God, just go away...’”

‘Jamaica Inn’ begins tonight at 9pm on BBC1