Louise Brealey talks new comedy Back, female Time Lords and the future of Sherlock

However, the arrival of his old foster brother Andrew (Robert Webb) causes problems as his returning sibling insinuates himself back into the family, leaving Stephen to wonder exactly what this interloper has planned.

Back has plenty of non-Peep Show-related fun to offer – and that includes the presence of Sherlock star Louise Brealey, who plays Stephen stay-at-home sister Cass in a part pretty far removed from her most famous role as lovelorn Molly Hooper in the BBC detective series.

To find out more, we caught up with Louise to talk all things Back, the fate of BBC3’s Clique, the casting of a female lead in Doctor Who and (surprise surprise) even managed to slip in a Sherlock question or two. Elementary, really.

So, Louise – how would you describe Back?

I've actually been getting into great difficulties trying to sum this up in a one-liner. Should've read a load of articles with David Mitchell being succinct, and pithy and funny about what it's about. So I'm at a loss.

Er... it's about a family and this chap who our parents fostered when we were little shows up and puts a spanner in the works.

It's brilliant for me to be doing a sort of out-and-out comedy, as it were. Because that's the first time in a long time I've done that.

Did you feel any pressure joining the Peep Show reunion of David Mitchell, Robert Webb and Simon Blackwell?

It's a tricky one isn't it, because Peep Show was epoch-defining. It simply was the best thing on telly for ages. It's so so so so so so good. That was 6 sos for you, by the way, for your tape.

Did I feel pressure coming to it? No! I was delighted, because they were my heroes. I mean yes, insofar as... “Better be able to not be s***, if you're working with people like them and Simon.”

I didn't feel pressure in terms of Peep Show's legacy, because that's not my cross to bear. I am not having that! I don't want it.

But in terms of working with people who you've admired for a long time, and just think are basically hilarious... yeah, it was a bit scary. But they are NOT scary as human beings. So that helped a lot.

What can you tell us about your character Cass?

Cass is still at home. She's in her mid-30s and she thinks of herself as this creative person, and yet hasn't left home. She thinks of herself as better than other people because of her art and her creativity, but she is still in the small town where she grew up.

I'm trying to think if it's appropriate for me to say... she's got that colour hair that quite a few very creative women from Bristol, Brighton, Camden have. That colour that they all have, and it's a statement of individuality, if you get my drift. Basically, all women with red hair are now gonna hate me... sorry. Sorry!

And I can vouch for the fact that it's an absolute b***h to get out! I'm currently apricot blonde which was halfway between. But it looks cool, I like the apricot colour that I am now. You might not know this but you have to keep dying red hair to keep it looking box fresh. Fades fast. Tricks of the trade.

But yeah, Cass is great. She's fantastically neurotic, as is her mother. She sort of vibrates at this very high frequency.

We don’t see that much of her in the first episode – do we delve into her character more as the series goes on?

Brealey (far right) with the cast of Back

I feel like everyone has a bit of a moment. It's a show about Stephen and Andrew. It's their story, but insofar as it's an ensemble we all get a bit of a go at it, I'd say. I mean yeah, absolutely, we're all there most of the time. There’s quite a lot of group scenes and riffing-type stuff.

I've got some really fun stuff with Rob's character, because as is pretty obvious in the first episode, [Cass] develops a large crush on him.

She sees him as a sort of passport to... well, away. Not to anywhere, just out. Because he's different and he represents who she would like to be. Who she thinks she is, actually – she's convinced herself she is that, and he's a kindred spirit.

Is the fear of being replaced or supplanted that Stephen worries about relatable, do you think?

I don't relate to it! Is the solipsistic reply.

I just think it's a brilliant idea. I think I buy it! I don't think it necessarily has to be massively relatable in order to be dramatically effective. I buy it. I think they sell it, I think it works, and certainly with their characters in the show it works a treat.

Because Stephen – David's character – is sort of checkmated all the time. He feels like he's always the only person who can see the truth. That's always good ground for laughs as well as dark elements.

I’m trying to think of a good example in TV or film for that…

Like Get Out, maybe?

Ha! Yes. That’s it – it’s like Get Out in Stroud. You can’t say that!

But it's that sort of sense of paranoia, and also... is he right? Or not?

It's ambiguous.

It is, which I like. So hopefully that'll keep people interested.

The first episode centres around a wake, with all the main characters present – are there more setpiece scenes like that?

There's loads of great funny stuff I think. It's subjective, innit? But I find it very amusing indeed. I really like Simon's writing! I think he's brilliant. Have you seen any Veep? I mean he's a genius. He's brilliant.

And also he's very smart, he rewrites all the time and he writes all people, so he sort of gets inside the characters. And you're like “Oh, that's how I've been playing her.” He's Good At His Job.

I don't know how to answer if there's any other great setpieces. Yes, there's loads of great, funny stuff to come.

Something else you worked on recently was Clique for BBC3 – any plans for that to come back?

I certainly think the intention was that it was going to return. I haven't talked to anyone about coming back.

I do feel, actually, that my character had sort of run its course on that. I feel like I had such a great, well, journey, I'm trying to think of a less clichéd way of putting it. But you know, there's a woman that begins as an absolute ballbreaker and ends in bits, and I'm not entirely sure how challenging another season would be for me.

But yeah, I definitely think they should do it again. I thought it was really fun, and I thought both the directors were brilliant. And all the young, beautiful girls were all flippin' marvellous, weren't they?

I had a great time working on that. And it was brilliant working in a Scottish accent. Really, proper challenge because you can't mess that up, otherwise you've no business being onscreen, opening your mouth and trying to be Scottish.

It was a really good part for me, because she's not meek in any regard. And because people tend to know me from Sherlock and Molly is... you know, she's got strength, but she's quite timid in some ways. She's mousy, isn't she, Molly? And this character is decidedly not that. She's completely alpha, which was so much fun.

Speaking of Sherlock – if the series does eventually come back, would you return?

Oh God yeah. Of course. I mean, it was such a big part of my life. You know, seven years, and a show that was as big as it was, in as many countries as it was....those things don't come around very often.

But aside from that, it changed things for me. And I love Molly, and I would love to play her again. Yeah, it's strange but I just feel very protective of that character. I feel very close to her. I don't know, she just means a lot to me, which seems a bit silly. She just does – I dunno why.

I think she means a lot to a lot of fans, too.

Well, certainly the correspondence would give you to believe something about her resonates with them. I think that's fair to say.

They do these little videos sometimes which people send me, which are these little mashups of Molly moments, Molly and Sherlock moments, and just put a song over the back, and all the rest of it. And it's kind of like they provide you with a showreel actually, except there's invariably some amazing power ballad about unrequited love or 'I've always been here for you' etc.

You don't often get to make a character over that amount of time. We all look like little buttons in the pilot. We all look so flippin' young. Little apple cheeks. Even Benedict's got apple cheeks. So yeah, it's quite nice to have had that.

I'd love to do it again, if Mark [Gatiss] and Steven [Moffat] were doing it. Obviously Ben would have to be doing it as well, otherwise it'd be a bit s***.

Unless it was a Molly-centric spin-off.

(laughs) Yeah.

And finally I have a slightly random question, but I feel like everyone else in showbiz has commented on this – what do you think of Jodie Whittaker being cast as the first female Doctor?

[You've asked] everyone else in showbiz! I think it's bloody brilliant. It's just really....ahhhh. I just had a lovely sigh of like 'OK cool, let's do it.' It feels great, doesn't it? And what was awesome was how after that, it was like an online talent show for complete twats to come out and offer themselves up.

And anyone who came up with anything remotely... 'Oh this is a trouser-rubbing game, this is for boys' – you just went 'Well, you're a twat. You're a tool, you're tool.' It was just like... ‘here come the tools.’

I think it's brilliant. I think it's exactly the right thing.

It reboots the show at a stroke, really.

Yeah, but it's just so wonderful that it offers... ROLE MODELS! I'm afraid role models are a very important thing, and for young boys to have a female role model like that is fantastic. And for young girls to have a female role model is really brilliant too.

So it's good news all round.

I think so – and she's also a bloody good actor, so that's good for the show. Another Good One.

This interview has been edited and condensed

Back begins on Channel 4 tonight (Wednesday 6^th September) at 10.00pm