By Editor,Stephen Armstrong

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Siân Brooke is shocked. She sits wide-eyed and cross- legged on a high-backed sofa and tries to find an answer to my question – is she ready for how famous she’s going to be?

She shakes her head.

‘I’m just happy to be working,’ she says. ‘I’m, like, this is great. When are they going to pull the rug out from underneath me?’ So I point out that the 45-year-old’s slow-burn career is about to explode.

BBC One is showing Trying, the sitcom about an adopting couple where she plays the main character Nikki’s smart and acerbic sister Karen. Channel 4 has her in season two of cyber thriller The Undeclared War with Simon Pegg. And the British Film Institute’s largest cinema recently hosted the launch of season three of her Belfast-based cop drama Blue Lights to a packed house.

The show, which won a Bafta for series two in May, is back on BBC One and is taking off in the US. America has already embraced Brooke in Sherlock and Game Of Thrones prequel House Of The Dragon. International medical schools, history departments and magazines from Vogue to Variety have even run essays on her performance in a doomed Caesarean section scene from House Of The Dragon. Not many actors get that kind of attention.

She didn’t see this coming. ‘I’m so shy. I was attached to my mum’s leg when I was a little girl, which makes acting a silly profession for me to have gone into,’ she says. ‘When I go to parties I’m always in the corner of the room. At the last one, my husband [actor and director Bill Buckhurst] and I sat in a corner and met a lovely bloke who was only there because he was a plus one. I could sit and observe people all day long.’

This series of Blue Lights is not going to help keep her out of the spotlight. She plays Grace, a former social worker and single mum turned cop. Having written the part as a Belfast local, writers Declan Lawn and Adam Patterson saw Brooke audition in 2021 and rewrote the part as English and rejigged the whole show around her. She’s always held the centre of the cast, but the new series delivers her strongest dramatic story to date. Her social-work life and police life collide when one of the kids she nurtured at a children’s home is caught up in a drug dealing gang. As Grace, her heart breaks so powerfully on screen that it’s difficult to tear your eyes away.

In person, she’s nothing like her wary on-screen alter ego or her breakthrough role in Sherlock, the crazed Holmes sister Eurus who flips through personalities like the pages of a magazine. She’s warm, effusive and likeable, dressed casually in a white T-shirt and jeans. As we chat, she leans forward to stress points or convey her strength of feeling – such as when she describes how cops in Northern Ireland thank her for representing them so accurately.

It probably helped that her dad was a police officer, making his way from beat bobby to CID detective. ‘When I was a child, I remember him being called in the middle of the night, having to go to work at 3am and deal with things most of us never see,’ she explains. ‘Then he’d have to compartmentalise that, come home and be my dad. He’s just matter of fact about it. He’ll talk about facing down guns like it was an everyday thing at work. But it helped me see behind the uniform with Grace.’

Sometimes she pulls away, retreating into the corner of the huge sofa – such as when she discusses her acting teacher and mentor Ellie Knight. She pauses and stays silent for a few seconds. ‘If I talk about her, I’m going to cry,’ she says, with a warm smile.

Without Knight she wouldn’t have become an actor. Brooke grew up in Lichfield, Staffordshire. Her parents were both from farming backgrounds so they valued a steady pay cheque. Her mum was a teacher – ‘both public servants, which gave me an awareness of being useful and making a difference. Then I went into the world of acting, where I am pretending to be other people for a living,’ she says, with a laugh.

Knight spotted her talent at Lichfield Musical Youth Theatre and helped her win a place at Rada – ‘I almost didn’t apply because it has “Royal” in its name, so I thought I had no chance,’ she says. ‘There certainly weren’t many Midlands accents.’ With Knight coaching her audition speeches, she made it in and headed south for a flat share with three people she’d met at the National Youth Theatre.

‘I was an 18-year-old Midlands girl in this flat on the Pentonville Road that was an offence to the senses,’ she says. ‘It had no windows, the tube went past outside and it was damp, but it was also wonderful.’

Living near King’s Cross in the late 1990s, the options for misbehaviour were enormous. Many children of cops go off the rails. But not Brooke. You get the sense she idolised her parents. She can even quote almost every line from The Princess Bride, the first video she remembers her dad buying with her, firing off a handful to prove it, including, ‘Hello. My name is Inigo Montoya. You killed my father. Prepare to die!’

‘My dad is a good guy, a decent person,’ she says, spreading out her hands. ‘My mum took me to all the youth theatre’s many rehearsals, every night of the week, even though she was juggling three kids and a job. They thought acting was precarious and they were absolutely terrified, so I took my education seriously.’

It paid off. She joined the Royal Court Theatre company alongside Rafe Spall and Daniel Mays, then was cast as the lead in the Royal Shakespeare Company’s 2004 Romeo And Juliet – ‘The third thing with “Royal” in the title,’ she says. ‘Where’s my damehood?’ That was where she met Buckhurst, who was performing in Stratford at the same time.

‘He wasn’t playing Romeo, that would have been too perfect,’ she says. They’ve been together ever since, have two sons – Ben, 11, and Archie, nine – and live in Southwest London where she trains for half marathons around Richmond Park.

She worked in theatre for years before the screen beckoned. Which brings us back to the autumn of Brooke and her flourishing roles on different channels. As the interview wraps, I bet her 50 quid her life will have significantly changed if I interview her again. ‘You’re very kind,’ she says, ‘but I’m just working and looking after my family, and I won’t tempt fate by taking any bets. I’m a pessimistic optimist. Always assume the worst but hope for the best.’

Blue Lights series three is on BBC One on Mondays at 9pm

Styling: Harriet Nicholson.

Hair and make-up: Maria Comparetto.