Unforgotten's Nicola Walker: 'My face either makes me look as though I'm deep in thought, or about to fight you'

“I think I’m finally growing into my face,” sighs Walker, 46 wryly. “I’ve always had a resting expression that either makes me look deep in thought or as though I’m about to fight you. 

“I’ve lost count of the number of directors asking me what the problem is when all I’m doing is sitting still and being.”

Walker is slighter than I expect for someone who played Gillian, Derek Jacobi’s agressive sheep farmer daughter in Last Tango in Halifax. She can reverse a John Deere (and trailer) across a cobbled yard like she was hefted to the hills rather than born in East London and raised in Essex.

Dressed in jeans and a vintage-style lacy blouse, Walker radiates a paradoxical combination of resilience and fragility and it’s this that makes her so watchable and probably why she has been cast as a cop six times. As well as playing the brooding, difficult-to-crack detective in Unforgotten, she has also played played a brooding, difficult-to-crack detective in River on BBC1 and the poker-faced  intelligence analyst Ruth Evershed in Spooks. 

No wonder then I expect her to be evasive and hard to pin down. To my surprise, she’s nothing of the sort in real life. 

“I could never be anyone I’ve played,” she confesses. “I am so not a detective; I can barely get 200 yards from A to B with the help of Google maps and I am just about the least observant person on the planet, so I never notice what people look like or how they walk or if they’re committing a crime in broad daylight.

“I live in dread that I might find myself in some sort of emergency and everyone will turn to me and expect me to know what the correct procedures are.”

Walker is funny, immensely likeable and with a sense of mischief entirely in keeping with her best friend, the comedian and Bake Off presenter Sue Perkins.   

“I remember being cast as a nurse years ago and the actor who was playing my tracheotomy patient wanted to nip out for a smoke. We were standing outside a real hospital, him with his pretend tracheotomy tube and his IV drip, puffing away and me in my uniform, when a senior nurse came past and gave us a huge telling off.”

So you explained to her that you were filming? And you all had a good laugh about it?

“No, I just apologised over and over,” says Walker, simultaneously stricken and giggling.

Walker’s CV is not confined to television; she won an Olivier for Best Supporting Actress in The Curious Incident of the Dog in the Night Time in the West End and last year she appeared to huge critical acclaim on Broadway in the Arthur Miler classic A View from the Bridge when it transferred from London.

Her recent ubiquity has led some reviewers to herald her as “the new Olivia Colman” -  a clumsy compliment and one which makes Walker visibly wince, not just on her own, but on Colman’s behalf. 

“I don’t think I’m the new anybody,” she says, slowly. “Besides, I’m older than Olivia; I’m sure she’d prefer the new her to actually be younger and far more glamorous than I am.”

Walker, the daughter of a successful scrap metal dealer, discovered her passion for acting early and attended classes at a local stage school. Academically bright, she went on to study at New Hall Cambridge, where she met the presenter and comedian Sue Perkins on her first evening.

“Sue was assigned as my College Mother who was supposed to look after me,” recalls Walker. “She introduced herself, asked to borrow my bike, got drunk and never gave returned it because someone had nicked it. Looking back, I let go of the bike thing a little too quickly, but then Sue is very easy to forgive.”

Perkins, who was in the year above, was already active in Cambridge Footlights and invited Walker along for a try-out on one of the comedy nights. “I became the 'falconer’,” says Walker, grandly. “It  was the title given to the person who went round afterwards with a black bin bag and tidied up.”

At one point Walker appeared on stage as Perkins’ stooge, spending an entire performance with a paper bag over her head, but mercifully found her true metier on stage in straight acting. A number of boundary-pushing student productions followed, and by graduation day she already had an agent and turned down a place at RADA.

One of her earliest gigs was a tiny role as half of an execrable folk duo in Four Weddings and a Funeral, but thereafter hers was very much the life of a jobbing actress. There were guest parts in Dalziel and Pascoe, Jonathan Creek and Pie in the Sky, but it wasn’t until 2003 and Spooks that she become a household face if not name.

“I’ve been doing this job since 1991 so it’s really weird to read about my 'overnight success' after years of graft,” she says amiably.

Married to actor Barnaby Kay, who appeared in Keneth Branagh’s Wallander series, she left Spooks after three years to have her son, Harry, in 2006, but later returned. Family life always takes precedence.

“Barnaby and I decide together who will take the plum acting job for three months and who will be entirely invested in de-icing the car and ensuring there’s milk in the fridge for cereal,” she says.

“It can be tough to turn things down, but as an actor, being in demand is a nice problem to have. It was my husband who persuaded me that we could 'do the Broadway thing’ as a family and I am so glad we made it work. They came over and stayed and Harry loved it and it opened my eyes to what could be possible for us; it’s all about teamwork.”

Teamwork is important to Walker; she thrills to the collaborative nature of performance. This is her second series of Unforgotten, in which she plays DCI Cassie Stuart alongside Sanjeev Bhaskar as DS Sunil 'Sunny’ Khan.

Its multi-layered complexity and slow-burning intense plotlines are a joy to watch - and to perform.

“I really like Cassie’s emotional temperature,” says Walker. “She’s solid, dependable; she has a moral compass that keeps getting interfered with, but there’s strong sense of justice at her core and we see enough of her personal life to make her believable.”

But for my money Walker’s portrayal of lairy, wary Yorkshire sheep farmer Gillian in Last Tango in Halifax was a tour de force.

“In the first series viewers didn’t know about Gillian’s hinterland, but I did,” says Walker. “People would come up to me and say things like 'she’s a game girl’ and I would feel pure anguish for Gillian.

“Only I knew about the darkness of her violent first marriage and how it coloured her attitude to sex. It was heartbreaking but at that stage I didn’t know if the audience would ever find out so I had to play her on level that hinted at her past without revealing too much.”

While the nation remains gripped to see what happens in this week’s final episode, Walker, along with the rest of us, is hoping it will be recommissioned. 

Rather shockingly, however, she has no confirmed projects in the pipeline (have we really run out of brooding, difficult-to-crack female detective roles? So soon?). Instead, for the next few months she will be reprising the altogether more challenging proposition of full-time mum.

“I was away so much last year, it’s nice to be at home,” she says. 

“These days I’m all about stocking the fridge with dairy products and doing the school run. If you look through my kitchen window you’ll probably see me high-fiving myself for nailing Motherhood.”

Unforgotten is on ITV 9pm Thursday