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What was it like playing her?

A terrifying hoot – she has a lot of lines.

How did you get into character/prepare for the role?

I based Deb on a little girl I used to know. You could see every emotion on her face. Guile, rage, confusion, fear. When she was cross, she scowled. When she was delighted, she beamed.

I used my real accent: Northamptonshire. It has softened over the years, so I sound a lot posher now, but it’s how my family speak and I’ve never had the chance to work using it.

Any funny stories from rehearsals or filming?

The scenes requiring our amazing intimacy coordinator, Elle McAlpine, were hysterically funny and genuinely not at all awkward. Poor Paul Bazely who plays Dev may have experienced some chafing.

What is the cast dynamic? Who was your favourite person to work with?

We are like a little family when we are filming. I feel very protective of Kat and Lizzie. And Paul is a wonderful human being and a phenomenal actor.

Are you still in touch with any of your co-stars?

Yes, we message all the time.

Josie (KAT SADLER), Deb (LOUISE BREALEY), Billie (LIZZIE DAVIDSON) in Such Brave Girls. © BBC/Various Artists Limited/James Stack

You’re perhaps best known for your role as Molly in Sherlock. What is that like to look back on?

Bittersweet because I don’t feel we finished it, and we have lost Una Stubbs. But it was incredible to be a part of what was really a phenomenon. It couldn’t happen now with streaming.

Any special memories from the show?

Too many. Having a candle in an egg custard tart (my favourite) on my birthday in Benedict’s trailer… Laughing and laughing with darling Una and Rupert Graves, who is a dreamboat.

You’ve also starred in the likes of Lockwood & Co, Brian and Charles and Back recently. But what has been your favourite project to date?

I loved working on Clique for the BBC a few years back. I got to play a hard-ass Queen Bee university lecturer in power suits who was afraid of no one, and then to completely fall apart. In an Edinburgh accent.

I loved Lockwood & Co. How does it feel for the show to be cancelled after just one series?

I felt so bad for the young cast, the crew, the fans and everyone whose livelihoods depended on the show coming back. It got such fantastic reviews and great viewing figures. I feel like the hoop it had to jump through for the streamer was just too impossibly small.

Any roles in the pipeline that you’re excited about? (If you’re allowed to tell us!)

I’m the lead in a lesbian chicken factory musical film called Chuck Chuck Baby.

Who has been your favourite actor to work with in the past?

This is much too hard. There have been so many that I admired, and some I now call dear friends. But my buddy Jeff Rawle I’ve worked with three times now, and we are trying to make it a fourth.

Which co-star did you learn the most from?

Antonia Pemberton, who played Nanny in Peter Hall’s Uncle Vanya when I was Sonya. She told me not to keep tomatoes in the fridge.

What’s your dream role?

I’m desperate to get back on stage. I’ve been doing film and television for the past seven years, but theatre is my heart and my home.

What’s a genre you’d like to do more of?

I’d like a good horror. I can’t watch them because I’m a scaredy-cat, but I’d love to be in one.

© Leo Staar

Do you get to spend much time at home?

Not enough. I’ve been gadding about.

Do you live in the town or the country? Which do you prefer?

I’ve lived in London since I left university. I live on a hill next to an oak tree, so it feels like we are in the branches. I can never leave London because I’d miss the culture stuff, but I am a woodland creature.

What’s your interior design style?

A mish-mash of old things I’ve found in auctions. Too many books.

How do you find balance in your personal and work lives?

I don’t.

What did you want to be when you were growing up?

An astronaut.

If you could give advice to your 15-year-old self, what would it be?

Don’t sleep with that guy’s flatmate when you are 21.

How can we all live a little bit better?

Choose love.

Anything fun in the pipeline – professionally or personally?

I’m going to run away to a southern European city for January and February to write.

Quick Fire

I’m currently watching… Only Murders in the Building

What I’m reading… We Have Always Lived in the Castle by Shirley Jackson

The last thing I watched (and loved) was… Silo. I love Rebecca Ferguson.

What I’m most looking forward to seeing… The Motive and the Cue with Mark Gatiss in the West End because I was away for its National Theatre run.

Favourite film of all time… Don’t Look Now

Favourite song of all time… ‘Disco 2000’ by Pulp

Band/singer I always have on repeat… Leonard Cohen

My ultimate cultural recommendation… Join all the museums and galleries

Cultural guilty pleasure… Overcooked 2. It’s computer game where you run around and try to make kebabs.

What’s next for me is… Walking my dog in Beckenham Place Park – it’s south London’s secret mini Hampstead Heath.

Watch

First pop-inspired fashion trends I adopted

I’m afraid I was a relentlessly unfashionable child. I was a square and listened to 10cc I’m Not in Love and The Eagles’ Desperado on repeat. I did love Robert Smith [from the Cure] but I didn’t wear enormous jumpers until my twenties.

First time I realised the BBC drama Sherlock was going to be a huge hit

The read-through was electric, which is not normal. Usually, it’s nerve-jangling because everyone is terrified they’re going to be sacked. A few weeks later I was watching the scene where Benedict first stuck his head round the lab door and said to Martin Freeman: “The name is Sherlock Holmes and the address is 221b Baker Street.” And I thought, yes it is. But really, I realised it was going to be huge when I was on early Twitter and the show went off. When Sherlock kissed [my character] Molly I got 60,000 followers in an hour.

Louise Brealey as Molly Hooper, right, and the cast of Sherlock

TODD ANTONY/BBC

First TV show I enjoyed

Like everyone at school I was obsessed by Jim’ll Fix It. I put two letters into one envelope to double my chances. One was to ask to meet John Travolta because I’d seen him star in The Boy in the Plastic Bubble, a film in which he plays this kid that can’t step outside a little plastic tent or he’ll die. The other was asking to meet the pop star Paul Young — I figured I had a better chance with him because he was from Luton. At least I didn’t do what my brother did and write to Jimmy Savile to ask to meet Rolf Harris.

First film I saw at the cinema

The first film I saw on my own at the pictures was Stand by Me at The Point in Milton Keynes. I had seen River Phoenix in the video for Ben E King’s single on Top of the Pops and was utterly love-struck. That was it. River was the only one for me. I still think River was the great acting talent of his generation.

First time I cried at the cinema

Watership Down. That was actually the first film I saw at the cinema. At the Palace in Wellingborough, when I was five or six. It was the first time I had any clue that creatures die. I was very affected by it — I called my next rabbit Bright Eyes.

First actor I admired

Joan Greenwood in Kind Hearts and Coronets. She was the single most beautiful woman I’d ever seen — and I was fascinated by her voice. I also loved Richard Burton’s voice, mainly because he narrated The War of the Worlds, my dad’s favourite album. I wanted to marry Richard Burton so I could listen to him all day long.

First thing I did to embody my new character Deb in Such Brave Girls

I started with her voice. I wanted to use the Northamptonshire accent. It’s the land of my birth and how my whole family talks except for me because I was a scholarship kid at a posh school, and I’ve never worked in it before. And then the clothes — Deb is obsessed with being feminine, so with her costumes it’s often about the cleavage. I think of her as a wily street rat in dangly earrings.

First famous person I met