"Why don’t we call it Potato?" Katherine Parkinson on new film The Guernsey Literary and Potato Peel Pie Society

A handsome, tear-jerking drama, it’s based on the posthumously published bestseller by American author Mary Ann Shaffer that was completed by her niece, Annie Barrows, after her death. Joining Parkinson in the stellar ensemble are Lily James, Penelope Wilton, Jessica Brown Findlay, Michiel Huisman, Matthew Goode and Tom Courtenay.

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With Mike Newell (Four Weddings and a Funeral, Harry Potter and the Goblet of Fire) in the director’s chair, the film stars James as successful writer Juliet Ashton, who is disenchanted with the post-war London party scene as she struggles for creative inspiration. On striking up a correspondence with Guernsey farmer Huisman, she is drawn to the islandbased book club of the title, while in flashback some closely guarded secrets are gradually surrendered to the island’s occupying force.

As an islander who provides homemade gin and a shoulder for James to cry on, Parkinson is the comic relief – the member of the society who’s dreaming of her Heathcliff while getting pie-eyed off her own supply. London-born, Oxford-educated Parkinson is rapidly becoming one of the most beloved faces on the small screen, as the Bafta-winning star of The IT Crowd, Doc Martin and Humans – for which she’s now completed filming a third series. The Guernsey Literary and Potato Peel Pie Society (in cinemas from Friday 20 April… yes, why don’t we call it Potato) kicks off a string of film roles for Parkinson, including highly anticipated Marie Curie biopic with Rosamund Pike.

Speaking to Radio Times from a sunny Georgia where she’s shooting another film, How to Sell a War for Rudolph Herzog (son of Werner), she’s warm and witty – and happy to talk love and literature. Parkinson was invited on board for Potato after Newell saw her in Dead Funny in the West End. With comedy, tragedy and romance all playing a strong part in the script, she relished the opportunity to mix things up. “The more well-realised a script, the more likelihood of it having both comic and dramatic elements. It should have, shouldn’t it?” she says. “Something like Humans, it was quite difficult to add humour to, but they did find some nice dry bits in the new series.”

However, nothing prepared her for Potato’s darker material. “I was just stunned with how little I knew about the occupation of the Channel Islands,” she says. “Filming scenes with the Nazis coming down the road… it really sent shivers down your spine.” So, what was it like working with such an esteemed cast? “Lily is easy to fall in love with and I had to sort of have a crush on her. But for me, getting to work with Penelope Wilton was amazing because she’s one of my favourite actresses and extremely good company. She really made me laugh.”

Shaffer’s novel might still be on her bedside table waiting to be read, but making Potato did inspire in Parkinson a fresh passion for literature. “It was while I was doing the film that I started to read for pleasure. My children [Dora and Gwendolyn with her husband, actor Harry Peacock] are five and three, and I’ve just started to get that slight sense of having a life back and not being exhausted every night.” Asked to name a favourite… book, not child… she plumps for Jane Eyre, which she only got around to recently. “I know I’m coming late to the party but I was so moved by it,” she says.

Making her way through the classics, just as they do in the film, was something Parkinson could finally share with her ex-English teacher mum. “My mum knew so much I thought I’m not going to even go there and now we’ve been able to chat about books, particularly Jane Eyre as she used to teach it.”

If Parkinson’s is technically the “best-friend” role, as the story unfolds we see a woman of substance behind the selfless support and humour, and her affection for her character is obvious. “Isola represents the independent survival spirit of lots of women in those circumstances. She makes gin and various tinctures and cures, and has made a good living for herself.” And, despite the poignancy to the scene where Isola confesses to Juliet that she’s never known real love, the actress sees the power of reading a little differently. “It serves to show how living vicariously through literature doesn’t necessarily have to be a sad thing,” she says. “I think when you’re really into a book, it’s not an imaginary consolation, it’s a real one. You can know romance through literature, and that is knowing romance.”

The Guernsey Literary and Potato Peel Pie Society will be released in cinemas on 20th April