Damaged detective Marcella is nothing like Saga from The Bridge says the man who created them both

“We kind of went the opposite with Marcella. With a lot of emotion, with much more vuln…” He gets tongue-tied. “I can’t pronounce that word.” Vul-ner-a-bil-i-ty. “That is a hard word, isn’t it? It must be one of the last ones that English kids learn!”

For a man whose job is to make up dark murder mysteries, he’s surprisingly jolly. At six feet eight inches tall and thickset, Rosenfeldt often punctuates his thoughts with a cartoonish, toothy grin, like a friendly Nordic incarnation of the Joker from Batman.

Yet this is the man who kicked off The Bridge with two corpses halved and then cojoined in the middle of the Oresund Bridge – and who has given Friel’s Marcella a much more dangerous medical condition than Saga’s apparent Asperger’s syndrome. “It is crucial to the plot,” is all that Rosenfeldt will say.

The opening episode sees Marcella Backland, newly dumped by her husband, go back to work as a detective after seven years’ absence during which she has been busy raising her kids.

“She’s chasing a serial killer who it seems is still at large – it was the last case she worked on,” explains Rosenfeldt. “Then we also thought, wouldn’t it be funny if Marcella had to investigate herself? That if, in one way or another, she incriminated herself into this plot line…”

Marcella is set in London and in the drama the city is a vivid, colourful, enormous place that’s intentionally a world away from the washed-out, empty, sludge-and-brown palette of The Bridge.

“It runs throughout the entire series – the visuals, how it’s shot, how it looks and how it sounds,” says Rosenfeldt. “ITV were very clear that they had no interest in a show that felt translated into English.” As a result, Rosenfeldt has had to learn aspects of British life and culture that are alien to him. For instance: the idea of taking a paying lodger into your home. “We Swedes would never do that,” says the 51-year-old firmly. “We are very private. With strangers, the first impression is always, ‘I don’t think I can trust this person.’ And I think in London, sometimes you just have to do it to make things work financially. It’s really, really expensive to live in Stockholm, but not so expensive that we need to take in strangers.”

Rosenfeldt has also been impressed by the ease with which the production team was able to assemble a racially diverse cast. Marcella’s estranged husband, Jason, is played by the black actor Nicholas Pinnock. “When I write a name like ‘Jason’ in the script for Marcella, it can be played by a black man. But when you write in Sweden a name like ‘Jonas’ it’s not a black man, because they’re just not called that. In Sweden, unfortunately, we have to think more about getting diversity. In the UK, you have it more naturally."

Jason forms the link between the murder investigation and another interlinked plot, about a shady property development company (headed, with delicious moral ambivalence, by Sinéad Cusack). And Marcella has to contend with Maddy – played by Laura Carmichael, very definitely no longer Downton Abbey’s Lady Edith – a student of criminal psychology, who also fancies herself an investigator. Plenty of hares running, then, for this first eight-episode series – and Rosenfeldt says that Marcella has been designed as a returnable show for ITV.

But before he starts to worry about series two, will Rosenfeldt put Saga Noren’s many British fans out of their misery by confirming what he said in Grapevine in the last issue of RT – that there is to be a fourth season of The Bridge?

“I’m not allowed to say,” says Rosenfeldt. Then, with that mischievous laugh. “But probably, yes.” Discussions, says Rosenfeldt, are ongoing with the Swedish broadcaster SVT and Denmark’s DR, and a decision will be made later this month. “And we have checked with everyone we need to get back – including Sofia Helin [who plays Saga] and Thure Lindhardt [her Danish colleague, Henrik].”

A pause between projects would be no bad thing for Rosenfeldt, who says that he has been working “around the clock” for the past few months. He grumbles good-naturedly that he’s out of shape because he hasn’t been running – the only physical training he enjoys, despite once having wanted to be a basketball player. Instead, when he was 21, he decided to focus on being an actor (at which he was “appallingly bad – I did it for the wrong reasons, I wanted to be famous”).

Today, Rosenfeldt lives about 20 miles outside Stockholm, with his wife and their 17-year-old daughter, Ebba. His 24-year-old son, Sixten, is at university in Gothenburg, and Alice, 21, is a diving instructor in Thailand. As well as TV, Rosenfeldt writes thriller novels (in which one of the protagonists is inspired by Robson Green’s character in Wire in the Blood). He had a successful run as a game-show host, and is a regular on Pa Minuten, Sweden’s version of Radio 4’s panel game Just a Minute – on which, over the past 21 years, he has developed his own rules.

“One of our panellists has a tendency… She’s not really hesitating, she’s not repeating herself, she’s not really leaving the subject. But the content of what she’s saying is absolutely nothing. It’s just words. Different words.”

So does Rosenfeldt buzz in?

“Absolutely, yes.”

But what’s the crime?

“The crime is you don’t make any sense. Anyone can say words. But you have to put them together into a sentence to be on that show.”

And do you win points?

“Sometimes. Sometimes not. Sometimes they think I’m just being petty.”

There’s that grin again. Rosenfeldt says that Pa Minuten is “the best job I have”. As he looks to the future, he won’t spill even the smallest of spoilers about the next series of The Bridge – “I’ve already said too much, actually” – but what about other projects?

Sofia Helin has now worked in Germany and Norway, and has said she’d love to come to the UK. Would Rosenfeldt consider writing a British series for Helin? “We haven’t talked about it. But hey, I would love to. I love working here, and I’d love to work with Sofia. It sounds like a match made in heaven.”

Marcella starts on Monday 4th April at 9pm on ITV