Holliday Grainger turned 30 last year in Dublin, while shooting her new film. In Animals, she plays Laura, a 32-year-old writer trying to balance the odd pressure of how she feels she should be behaving, and how she wants to behave. “I think there is a pressure on people,” Grainger says about reaching that age. “It’s – what are you doing with your life?” Though the film is set against the sort of dedicated partying that is outrageously fun, until it isn’t, Animals is also a subtle, unsettling look at the expectations placed on women by themselves, their friends, their families and lovers, as well as the world around them.

“It was this weird day,” Grainger recalls of her 30th. She and her co-star Alia Shawkat, who plays the more hedonistic Tyler, were filming a scene in which they visit Laura’s baby niece for the first time, nursing bone-crushing hangovers. “And they have an argument about joining the baby club or not.” Two of Grainger’s best friends, and their own babies, had flown out to visit her. “So on set were my best friends, their babies, and we were filming a scene about the choice between having a baby or not, and turning 30.” The director, she says, was excited about the synchronicity.

Grainger, who grew up in Manchester, started acting when she was five, in the BBC’s All Quiet on the Preston Front. “I’m still in touch with people from that first job. I loved it. I was in the adult world,” she says. She is composed yet slightly reserved, and has the air of someone suited to being in the company of adults from an early age.

Recently, she has been playing the private-investigator-in-training Robin Ellacott in the BBC’s wildly popular Strike series, which has adapted the Robert Galbraith (AKA JK Rowling) thrillers for Sunday-night primetime, and she is also starring as Anna Paquin’s lover in Tell It to the Bees, a 1950s-set slice of magical realism. “It’s amazing now how all of the scripts I’m being sent are contemporary TV or independent film, it’s not period drama. I don’t know if that’s just the fashion of the industry right now, or how people see me.” For a long time, Grainger was the go-to girl for a corset or a bonnet: she was Lady Chatterley; she did The Borgias; she appeared in Anna Karenina, Bel Ami and Jane Eyre.

“For most of my teenage years I was the northern best friend. And then someone was like: ‘Oh, she can do RP!’” She says this in a fancy accent. “Then it was like, you can be the posh lead. Then it was the posh lead in a corset. I remember a Skype meeting once, with some director, and he asked: ‘Can you do contemporary?’ I was like: I’m not speaking to you from the 1900s right now.” She gestures towards her outfit – jeans and an off-the-shoulder top. It is very much not a corset.

Grainger as Robin Ellacott and Tom Burke as Cormoran Strike in The Strike. Photograph: Steffan Hill/McAinsh/PA

We are in a hotel room in central London, and Grainger has just returned from a long lunch with Shawkat. The two of them seem particularly devoted to Animals, an adaptation of Emma Jane Unsworth’s cult novel, which Sophie Hyde, the director, sent to her to scope out her interest. “And I read it in a day. I’m from Manchester, it’s set in Manchester, and it’s very rare that you have a chance to be part of a project that is so close to your roots.” She felt as if she already knew Laura and Tyler. “I knew all of the references to locations in Manchester. You are my friends, you are people I know. And I’ve never had chance to portray that on screen.”

But the film is set in Dublin. “Well, yes.” She got a phone call from Hyde saying that funding wasn’t quite working out in the UK. They had to decide whether to shoot it in Dublin and pretend it was Manchester, or shoot it in Dublin, and let it be Dublin. “I think Dublin and Manchester are so easily transferrable, because Dubliners and Mancunians do have a similar vibe. There’s a similar musical and literary heritage. A strong cultural heritage and a strong cultural identity. And there’s a pride in both cities.” Grainger’s accent, a little softer in person than it is in Strike, gets slightly stronger. “It’s such a cliche, ‘people up north are friendly,’ but there is a sort of camaraderie, inclusivity and a no-bullshit that Dubliners and Mancunians share.”

At the time of shooting, she says, the film started to make more sense in Dublin. The campaign to repeal the eighth amendment was at its peak and the vote on legalising abortion in Ireland was about to take place. “It’s this story about women’s life choices, and you’re getting to an age where you’re [wondering], am I having to make them because society tells me to or because I want to, because I’m ready for the next stage, whatever that is?”

Playing Laura had its own particular demands. First, she had to play drunk, a lot, a notoriously difficult thing for an actor to pull off. How was it? “That’s a question for you,” she replies. Whether staggering around a nightclub dancefloor or throwing up the morning after, she is very convincing. “But I guess Laura and Tyler are good at drinking. It’s a skill, and they have it. They mediate the alcohol with other substances, so you don’t really see them wrecked.” Also, she says, there’s an easy path to on-screen drunkenness. “Basically, just spin around before the take.”

Grainger had a few sessions over Skype with an Irish dialect coach. “A lot of it is just, listen and repeat, listen and repeat. And then you’ll get to the point where you have the bravery to just get out and speak to cab drivers and see what their reaction is. That’s the only gauge.” She kept the accent up for the duration of filming and, halfway through the shoot, she found herself chatting to a man in the pub. “He said, so where are you from? And I was like: ‘Oh, my accent’s shit.” And he said: ‘Are you northside or southside?’ Of Dublin! I was like: ‘Yesssss!’” she laughs. “You don’t want to be that English girl who came in with a shit Irish accent when they could have just cast someone from Dublin.”

• Tell it to the Bees is released in the UK on 19 July and Animals on 2 August