Nicola Walker, star of Unforgotten and The Split, returns to the theatre | Nicola Walker

A lot of actors would “go into a tailspin” if they lost their director for two weeks during rehearsals for a big stage role, said director Dominic Cooke. But not Nicola Walker. When he returned to the National Theatre for rehearsals of The Corn is Green after a fortnight out with Covid, exclaiming how terrible it was that they had lost so much time, his lead actor put him straight. “She said, ‘Well, I’m not in Ukraine’. And I thought, ‘Yeah that’s you. You’ve got a sense of perspective about it.’”

In showbusiness, where being grounded is not a common trait, Walker’s level-headedness makes her stand out. “It’s very straightforward for her. She sees where she is in the bigger picture,” said Cooke. “And that’s an admirable quality in anyone but especially in the crazy world of entertainment.”

After decades of gaining growing recognition, this promises to be a big week for the 51-year-old, best known for her roles in BBC dramas Spooks and Last Tango in Halifax, as an MI5 analyst and a farmer respectively, and as a detective chief inspector in ITV’s Unforgotten. She’s playing divorce lawyer Hannah, whose marriage (to Nathan, played by Stephen Mangan) continues to unravel in the final season of The Split on BBC One.

Meanwhile, off screen, she is in the process of making a long-awaited return to the stage as a visionary teacher in The Corn is Green, the semi-autobiographical 1938 play by Emlyn Williams, which is at the National until 11 June after a two-year delay caused by the pandemic.

And later this year, she’s starring in another relationship-centred BBC drama, Marriage, with Sean Bean.

As Gillian in Sally Wainwright’s family drama Last Tango in Halifax. Photograph: Matt Squire/BBC/Lookout Point

Cooke, who described working with Walker on the play as “a revelation”, said he had never seen her do anything like it. “It’s a different kind of role for her. But she is, I think, made for it,” he said, adding that she seemed “incredibly comfortable” in the starry role, which has been played on screen by Bette Davis and Katharine Hepburn.

“The thing is, she’s done so much,” said Cooke, who directed Olivier award-winning productions Ma Rainey’s Black Bottom and Follies and the film adaptation of the Ian McEwan novella On Chesil Beach. “Before she did television, she just did years and years of theatre. And when you get that level of experience in an actor, it’s like working with a virtuoso, they have a lot of strings to their bows. They have a lot of resources, and she’s got that.”

Her stage credits include an OIivier award-winning turn in The Curious Incident of the Dog in the Night-Time, winning best supporting actress in 2013, and Beatrice in Ivo van Hove’s acclaimed 2014 Young Vic production of A View from the Bridge, which transferred to the West End and Broadway.

Cooke sees her having the kind of trajectory as Judi Dench, who at 87 is still going strong. “The sky’s the limit for her [Walker] and there are going to be amazing opportunities for her in the coming years. She’s definitely got that sort of Judi Dench national treasure potential.”

Yet it took a long time for Walker to reach household-name status. Like Oscar-winner and fellow Cambridge graduate Olivia Colman, she had turned 40 before her career started to fly.

In her 20s, Walker was warned by older female actors that getting work would be tough once she turned 40. But now she is busier than ever. “The past 10 years have been the best of my career,” she said recently. “I didn’t see it coming.” The year 2020 was her quietest since giving birth to her son, Harry (who she named after Spooks character Harry Pearce) in 2006.

With Sanjeev Bhaskar in ITV’s hit detective series Unforgotten.
With Sanjeev Bhaskar in ITV’s hit detective series Unforgotten. Photograph: ITV

Her home life, with her husband Barnaby Kay, also an actor, and son in north London, is said to be “grounded, regular and sane”, and an important part of who she is. Harry, she recently claimed, had not watched any of her work in full because he found it strange seeing his mother on TV. Fortunately, her husband, who she said was “very supportive”, watches everything.

The most commonly used adjectives adopted by those who have worked with her seem to be fun, brilliant, intelligent, extraordinary and kind.

Dee Koppang O’Leary, who directed her in The Split, said her performances were so layered and nuanced that she didn’t want scenes to end. “She has the most emotional and emotive face I have ever seen – and when the camera is on her, you don’t ever want to call cut.”

Chris Lang, the writer of Unforgotten, first met Walker in 2007 when she featured in his show Torn. He knew her from Spooks, but he wasn’t prepared for how good she would be.She had just had her son, and it was almost her first job back from maternity leave. I remember auditioning her and just thinking she was extraordinary, an amazing actress,” he said.

They went on to work together on A Mother’s Son in 2012 and later on Unforgotten, first shown in 2015. Although he wrote the role for her, she was then still not considered a leading actress, he said. “She was just on the verge of making that leap. But I knew from the first time I worked with her that she could carry a show completely.”

With Phoebe Fox and Mark Strong in Ivo Van Hove’s acclaimed production of Arthur Miller’s A View from the Bridge.
With Phoebe Fox and Mark Strong in Ivo Van Hove’s acclaimed production of Arthur Miller’s A View from the Bridge. Photograph: Tristram Kenton/The Guardian

Part of her appeal, he said, was that she was an empath – both on and off screen. “You identify with her and you see yourself in her. I think that’s quite a rare gift and not many actors have it, but she has it in spades.”

Such is her ability to make others believe in her characters that Unforgotten director Andy Wilson, said when her character, DCI Cassie Stuart, died, he had to watch the scene 100 times during editing, and cried every single time. “That’s a tribute to her. Because the person she created in Cassie was so real to me,” he said from set while filming the new series.

Wilson said that Walker had changed perceptions of women on TV through the role. “She’s a female lead who’s willing to show you her character’s vulnerability and weakness. She’s willing to be vulnerable and she’s also willing to be the leader,” he said. “It’s a rounded character in a way that I don’t think we’ve really seen before.”

He said Walker made him laugh when the bodies arrived on set, when she would always be “vaguely disgusted”. But, he said, the most memorable thing about her on set was “her explosive laughter”.

Walker, who was born in Stepney, London, to a father who was a scrap metal dealer and a mother who was an interior designer, started acting when she was 12 at youth theatre but didn’t imagine doing it as a career. As a child she loved black-and-white musicals with stars such as Fred Astaire, Ginger Rogers and Gene Kelly. After attending a private school in north-east London, she became the first in her family to go to university. At Cambridge she was taken by her friend Sue Perkins to the university’s Footlights drama club.

She has always been true to herself, said friend and creator of Spooks, David Wolstencroft, who remembered first meeting her at a Footlights comedy event. “The overwhelming impression I had of Nicola was that, in stark contrast to a lot of us at that time, she didn’t appear to be trying to be anybody but herself – which, given her talent and career path, sounds paradoxical. But she simply was who she is.”

He first saw her on stage in 1990 at a Footlights revue and noted that her “heart and precision was already there”.

Wolstencroft said he remembered “the sound of her and Sue Perkins laughing constantly”. After university, Walker got a place at Rada but decided not to go because of the cost and because she was, she has said, “in a rush to get going”.

With Steve Pemberton in the comedy anthology series Inside No 9.
With Steve Pemberton in the comedy anthology series Inside No 9. Photograph: Sophie Mutevelian/BBC

Despite this, many of her colleagues praise her technique. Last Tango in Halifax writer Sally Wainwright said: “There’s something about the detail that she puts into every beat, into every moment, and then makes it look effortless. There’s always a sort of gravitas to any scene that she inhabits.”

After university, Walker carried on acting in friends’ plays above pubs. And it was in a play at a pub, alongside Rachel Weisz, that she got the attention of an agent.

She struggled to get TV parts in those early days but did appear as one half of the “frightful folk duo” in Four Weddings and a Funeral. Wolstencroft remembers seeing it and thinking “Well, that makes total sense … Off she goes!” He later went on to work with Walker on Spooks, in which he described her as “a centre of gravity for the show”, and in Shooting Dogs, a film about the Rwandan genocide that he wrote.

What next for Walker? Does the US beckon? “She’s a rising tide that lifts all boats. I’d love to see her in a big US show. If I’m ever lucky enough to find myself behind the wheel of one of those, I’d beg her to come and play,” said Wolstencroft.

But the actor’s approach to this is, characteristically, far more down to earth. When asked recently whether she was tempted by Hollywood, she claimed she mainly associated it with watching Marvel films with her son. She has also said she would like to work with Perkins again. She recently said that she was “practical about acting”, adding: “My dream role is always the job you get next.”

Producer Jane Featherstone, who has worked with Walker on Spooks, River and The Split, said her biggest motivation was great writing and colleagues. They first met on ITV drama Touching Evil in 1995 when she was fresh from university. “She was just amazing in the audition, and ITV took the punt on her and we got very lucky” she said.

Walker’s ability to be simultaneously ordinary and exceptional made her stand out, she said. “She’s quite unusual, she’s quite special but also extremely relatable, and that’s a rare thing. We’re lucky when we get ones like her, honestly.”