Timothy Spall's new crime drama filmed entirely in Wales

Spall portrays John Chapel, the favourite TV character of Det Sgt Janie Mallowen, played by Keyworth.

Det Sgt Mallowen idolises Chapel after his TV show Caesar helped her through one of the darkest times in her life.

But she begins to discover that Chapel the man is not quite the same as Chapel the actor.

The show's writer, Paul Doolan, admitted to being a "bit of a murder-mystery obsessive".

"I liked the idea of a TV actor who played a detective, and a fan of them, and the awkward relationship, but I couldn't really get beyond what else was funny about that.

"Then I thought 'what if they solve murders?', which is all really meta, and then started plotting it based around that."

In the show, Spall's character first comes across Det Sgt Mallowen when his neighbour is murdered and she arrives to investigate.

"All relationships, you need that conflict, you need there to be stakes and you need a power dynamic," said Doolan.

"Having him being famous and her being a fan, you only need to know that and straight away you get what all those dynamics are.

"The physical differences, the generational differences, he's English, she's Welsh – there's just piling as many opposites in together and have them be spiky to each other."

Being an actor playing an actor gave Spall "some opportunities to illustrate that pretentious side of it and if I'm taking the mick out of anybody it's myself", he laughed.

He was full of praise for his co-star Keyworth, of Misfits and Hidden Fame, whom he first encountered when she starred in a West End production of To Kill a Mockingbird alongside Spall's son, Rafe.

"I thought, bloody hell, she's good. Then a couple of years later here we are in this odd-ball double act," he said.

Her character, Det Sgt Mallowen, is "very practical", he said, adding: "She's procedural, she's a policewoman and has to go through all sorts of things.

"They are quite candid to the point of rudeness and offensive with each other but they always somehow are reliant on each other. They'll never admit that they have affection for each other."

Behind the humour, there are darker sides to the show.

Det Sgt Mallowen lost her best friend to suicide aged 18 and the drama portrays how she deals with that trauma.

Keyworth, from Aberystwyth, thinks plenty of people can relate to using escapist TV to cope with tough times - as her character did with Caesar.

"It's like her hero has come home to roost, but then she has to deal with the reality of [Chapel] is not actually Caesar, and in fact can be a little bit annoying.

"They've both been really lonely for a long time and there's a level of kindred spirits that meet.

"Then ensues a lot of comedy because they have very different approaches to life."