Death Valley's Timothy Spall and Gwyneth Keyworth on their 'delicious' crime comedy

TIMOTHY: "The first time you meet my character is quite odd — it's probably going to wrong-foot the audience a bit because you start out in a contemporary setting, and then you'll see this period TV show Caesar, which was made at the beginning of the noughties but is set in 1959. The show was a huge hit, and as is the way of things, most people under the age of 50 have no idea of it! Since then, John's been living as a recluse in this beautiful place where his wife came from, and Janie meets him when she's making inquiries after his neighbour is murdered..."

GWYNETH: "Janie is a young police officer trying to make her way up the ranks — she takes her job very seriously, but she doesn't take herself too seriously. She has a bit of a blind spot when it comes to emotional connections, and that's because she's still grieving the loss of her best friend, which she went into a bit of a depression about and hasn't really recovered from. During her depression, Janie became obsessed with Caesar, and has based a lot of how she likes to work procedurally on this crime show. A few years later, there's been a murder in a property developing firm and she's calling on the neighbours to see if anyone knew the deceased and if anything suspicious has arisen — and it turns out that John Chapel lives in that house!"

GWYNETH: "For a brief moment, Janie completely forgets that she's a police officer! She sees her all-time hero in the house and she's like, 'oh my God, it's John Chapel, I love you!' That's how they meet, and then John sort of suggests that, as an actor with an emotional understanding of character and what drives people to do things, he might be able to help her — and at this point, Janie's so star-struck that she's like 'yep, great! Let's go!' And then she comes to her senses and goes, 'actually, this isn't appropriate, you're just a member of the public, you're not Caesar' — but it's too late by that point!"

TIMOTHY: "He starts very eccentrically coming up with all these things that I think she calls 'the ramblings of the local hermit', but they have this instant recognition of each other — they're immediately rude and immediately candid, and they kind of get each other straight away. It begins this affectionate, but never sentimental, mutual reliance on each other, as he uses his psychology and his eccentric view of the world, and she's able to draw on that, and she's quite an eccentric character herself. But she's kind of unleashed a monster in him!"

TIMOTHY: "Every time she says 'go away', he turns up again! People recognise him occasionally too, so she's terrified that people are going to spot the fact that they're a double act."

GWYNETH: "Janie's just trying to keep her job, and John keeps just turning up and getting involved in all of her cases! He literally tuns up at the police station and she's like, 'you can't be here! You're not meant to be involved!' Their dynamic is almost sibling-like, despite the age difference."

GWYNETH: "Working with Tim is the dream — he's very good at acting, isn't he?! And he's a really lovely human being, he doesn't take himself too seriously, he's joyous to have on set. It was brilliant to learn from him. Also, he drinks a lot of fizzy drinks, and that really opened up a gateway for me, because now I can't live without Fanta Limon — it feels like you're on holiday all year round!"

TIMOTHY: "Gwyneth's a fantastic actor, she's brilliant at comedy and drama. I saw her on stage because I went to see my son [actor Rafe Spall] in To Kill A Mockingbird and he was playing her dad, she was playing a child in it and she was brilliant. That's where I first saw her and I thought 'wow, she's good' — and a little while later here we are in this new oddball double act!"

TIMOTHY: "Of course! He's quite experienced and he's done an awful lot, so he's quite conceited and arrogant and a little bit in love with the idea of being an actor, but because he has't worked for a long time, I think he's terrified that he might have lost it. There's lots of examples of over-flowery language, making things seem like they might be equivalent to warfare when basically he's just doing a bit of Shakespeare, so there are some wonderful opportunities to illustrate that, shall we say, slightly more pretentious side of it. But if I'm taking the mick out of anybody, it's myself!"

TIMOTHY: "What I love about this show is that there are moments where it's aware it's being a whodunnit and subverts itself through the eccentricity of the duo and the circumstances they find themselves in. There's one set in a country house at a murder mystery event, so that's almost a trope within a trope — they're all genius!"

GWYNETH: "Yeah, I've never worked on anything like it — there are elements that are familiar to everyone, but it's got these extra flavours added in that make it more delicious. If you like cosy crime drama, you can watch the series and you will have that, but you're also getting bang for your buck because you're also getting Tim Spall giving beautiful emotional levity to the whole thing, and it's also really funny. It was the best job I've ever done, and I'm really proud of it — I just hope audiences like it now!"