The Traitors: Why viewers became so loyal to the BBC reality series

Depending on your television diet, your favourite reality competition might take place in a Spanish villa, the Australian jungle, a Hertfordshire ballroom, or a giant tent filled with ovens and self-raising flour.

But recently, an increasing number of viewers have instead been escaping to a Scottish castle with Claudia Winkleman and 22 members of the public who just want to avoid being murdered.

Fortunately, the murders committed in BBC One's The Traitors are metaphorical, but the bloodless backstabbing has nonetheless inspired a fiercely devoted following since the series launched in late November.

"It's got a fresh formula which nobody else has really done," says Harrison Brocklehurst, pop culture writer for the Tab. "And in a time when a lot of reality TV has blurred into one, all following the same formulas with who they cast, I think the Traitors really stands out as unique.

"They have a really wide range of ordinary people, different ages, races, sexualities, it makes for a real smorgasbord of personalities. What's made it so fun is it's always the people you don't really expect who have played a blinder."

The format sees the players gathered at Ardross Castle in the Scottish Highlands. Upon arrival, three of them are told secretly, via a squeeze on the shoulder from Winkleman, that they are traitors.

The aim is for the other contestants - known as faithfuls - to root out the traitors, provided they can survive themselves. The traitors can "murder" one player every night, removing them from the game.

A possible jackpot of £120,000 can be won by the faithfuls who make it to the end. However, if any traitors make it to the final undetected, they take all the money instead. The concept is delicious, and makes for addictive viewing.

The format was developed by Dutch broadcaster RTL and the original version, De Verraders, launched last year. RTL's director of content, Peter van der Vorst, says the initial idea was pitched to them three years ago, which they began developing.

"We played it with my management team in my backyard. And it worked!" he recalls to BBC News. "Within seconds the whole dynamics within the team changed. We ordered it on the spot."

He adds he is "really enthusiastic" about the BBC's version. "In the Netherlands we played it with celebrities, in Britain you do it with unknown people which works really well too," he says.

"So that could be an inspiration. Our British colleagues also added some game elements that will be useful to us."

It's clear from the prime-time scheduling the BBC has confidence in the UK adaptation. But the corporation's director of unscripted Kate Phillips, who brought it to British screens, tells BBC News: "Every time you take a new show, it is a punt, because there's no guarantee it is going to work.

"I don't think there was any doubt that the series would be good, but because the television landscape is so competitive now, the only worry I had was, 'Will it break through?'"

Catch-up viewing has played a key role in the show's momentum. "We knew it would be word-of-mouth, we wanted people to talk about it and pass it on and that's what's happened, it's a grower," Phillips says.

The Traitors maintains a constant air of suspicion even as bonds start to form between the players, nearly all of whom have huge personalities. Nobody gets through a sentence uninterrupted; the atmosphere is one of chaos and tension.

In the absence of concrete evidence, the contestants come up with theories based on each other's real-life jobs, facial expressions, body language and behaviour during the physical challenges.

Amanda in particular has become the show's breakout star. Assigned a traitor in the opening episode, she left viewers awestruck by skilfully using her kind nature and lilting Welsh accent to mask her deceit.

The format feels fresh, yet familiar - as if several successful reality show concepts have been combined. The contestants spend their days in close quarters, much like Big Brother, while the outdoor physical tasks are reminiscent of I'm A Celebrity.

"Inevitably, there will be a few [familiar] things," says Phillips. "You might think 'Oh I've seen a task a bit like that before', but I think nobody has ever seen a show quite like this. I think partly that's because of the gothic melodrama, the capes, the fires, the night time, make it feel very distinctive."

Plus, the core game itself is recognisable to viewers. It is similar to card games such as Mafia or Werewolf. Camilla Long of the Sunday Times likened it to wink murder.

"The main crux of the game is familiar to different people," says Brocklehurst. "I did theatre at university and college and we played a variation of it as a warm-up game."

Reviews have been increasingly positive as the show has progressed. The Guardian's Rebecca Nicholson said: "The BBC has waited until the end of the year to slide out what is turning into one of its most exciting series in ages.

"On paper, it sounds perfectly fine if relatively tepid. Cut to three weeks later and I am watching each episode with multiple text chats on the go, as if in charge of an air traffic control tower at Heathrow. This is masterly reality TV."

Its viewing figures paint a mixed picture. The opening episode attracted 2.9 million viewers - a respectable but not outstanding figure.

It has, however, grown its following via iPlayer, with many viewers racing to catch up as word has spread. The first episode has now been seen by five million viewers. More complete data will become available in the coming weeks.

The thrice-weekly broadcast rollout means The Traitors is a less overwhelming proposition than others. "It doesn't have the intensity of Love Island, which is on six nights a week," says Brocklehurst.

He suggests social media has stimulated catch-up viewing. "The memes and everyone live-tweeting it has played a big part in its success. Nobody wants to miss out on a reality TV show that everyone is talking about."

Phillips agrees, adding: "When I'm looking at a new show, the other thing I always say is 'What are the Gogglebox moments?'

"So if I was watching that show, would there be several moments that would give me a strong reaction? Would it be a show that would make it on Gogglebox because it would be a gift to all those people responding?"

It's perhaps telling that The Traitors has indeed featured heavily on Gogglebox (which is also made by Studio Lambert, the production company behind the British adaptation of The Traitors).

Many viewers are enjoying seeing a darker side to Winkleman, who initially turned down hosting the show until producers showed her the Dutch series.

"They sent me it. My kids did not get fed, I didn't brush my teeth, I watched the Dutch version weeping because I loved it so much," she told Graham Norton.

"Every other game show is about luck or about general knowledge. This is purely a game of charm, nous, of being wily."

Philips, who has worked with Winkleman for many years, says: "I think Claudia's a perfect host. We're seeing another side to her, she's got that wit and that drollness, but she is a tough Claudia, she can be a bit severe and scary, and she genuinely cares about the show and its contestants."

There is a noticeable difference with the contestants on other shows, notes Brocklehurst. "It doesn't feel like people are in there to become influencers," he says. "I think the public are a bit over that."

The players' entertaining reaction to the twists and turns of the game can be credited to "the joy of the first series", suggests Phillips.

"It's like when Big Brother first launched," she says. "These contestants are coming to it new and they're not sure what's going to happen."

"Already we're thinking that if we do have a second series, they will have to cast it a bit differently, because contestants will be coming to it with more knowledge."