“I just locked eyes with a man and I think he thought I was really eyeing him up.” Actress Alice St.Clair and I are at a little Austrian cafe in Angel. She’s grinning from ear to ear and blushing profusely, half mortified, half amused as she looks out of the window posing for photographer Eliza Power. “Oh God! I was looking really dreamily into his eyes.”

 I’ve never interviewed anyone who talks as happily and easily as Alice. Her stories of living in America and filming in Bristol takes us from New York’s neatly laid out streets to LA’s obsession with cars to a field hospital in France. Her optimistic cadence is exactly what’s needed on this freezing London morning as we navigate the history and the psychology of her latest project: BBC One’s World War One drama The Crimson Field.

The Berkshire born actress, who most recently starred in Aaron and Billy Sharff’s Before I Sleep, will feature in the six-episode period drama alongside Suranne Jones, Hermione Norris and Oona Chaplin. She plays a young nurse dispatched to France as part of Britain’s Voluntary Aid Detachment.

Dressed simply in black, sporting a gold necklace and spiky, loose topknots, there’s an experimental, casual edge to Alice. Having grown up with two brothers and a sister, she shipped herself to New York at 16 for drama school and lived in LA for a while (“I don’t understand the driving culture…how much fun can that really be?”) before returning to the UK.

“I’d 100% encourage anyone thinking of going to school in there to do it” she says of New York, “it’s an amazing city and I really hope I end up going back there but also just as a change, to get away, it really made me grow up.” Leaving home to live independently at 16 has to be scary though? “Weirdly, I never felt vulnerable,” she says, “it may have been that teenage fearlessness. If I had to go over there now, I’d feel a lot more nervous but back then, I really didn’t feel intimidated at all.”

Home however, is still Berkshire. “I’ve been flitting around for a while, but home is still my family’s house. We all go off and do our own things but that’s home. Filming the show in Bristol meant I got to see my parents a lot, which was good, all my old stuff is there, my old memories. That said, when it comes to cities, I know New York a lot better than I know London. It helps that Manhattan is just so easy to navigate!”

Between coffees and an unexpected launch into an appreciation of all things Austrian including Stollen, she tells me about her character in The Crimson Field. “She’s called Flora and she’s not really old enough to be there,” Alice explains. “She’s only 18 but the volunteers they sent to France had to be at least 23 with three months hospital experience, so she locked herself in her room and pressured her family to lie for her.” She sounds delightful. “Ha, yes, a lot of the lines could come across as spoiled and a lot of the other characters think she might be. But she isn’t and she changes as the show goes on.”

And Flora is easy to relate to, Alice insists, “She’s so very rushed, she finds she can’t do a lot of things she thought would be easy but she sticks with it. She learns to really takes her time, she gets the task done and becomes really quite good at it. She’s got perseverance. I can relate to that”.

The two seem to have even more in common when it comes to how easy they are with the people around them. “Flora’s also very good at talking to people freely. Like her patients who come in with these gaping wounds. She’s not like the others who can only focus on the injuries, she talks candidly with them and puts them at ease. I can also relate to her feeling of being foreign. She’s landed in France in this strange situation, she’s nervous and lonely. I’ve certainly felt that before.”

 Though still at the start of her acting career, Alice is gathering a stronger idea of the kind of parts she wants and actors she takes inspiration from. “One of the things I really admire about Hermione [Norris] is that she has this quite young family and yet she manages it all so seamlessly. Suranne [Jones] is brilliant, she has time for everyone, she’s so welcoming. The more I look at the actors I’ve always admired, the more I realise it’s because they are just constantly doing all these different roles. Do you know Juno Temple?” And so follows a lengthy, excited discussion about how admirably left-field Temple’s work has been since she did Atonement. Forever optimistic, still carrying more than a bit of that teenage fearlessness, get ready to see Alice St. Clair hit your screen in the most flavoursome, risky roles.

The Crimson Field will air on BBC 1 in April.

Photos: All rights reserved ©Eliza Power