Murder, betrayal and lies - why The Traitors appeals to our dark side

The hardest thing with lie detecting is knowing how people behave normally, according to Prof Wiseman, who has written about the psychology of magic and illusion, deception, luck and self-development.

"What we're quite good at is, when it's friends and partners, we know their truthful behaviour," he says. "And you're looking for people departing from that."

For example, when TV presenter Kate Garraway stood accused of being a potential traitor for her excessively theatrical reactions, she defended herself by explaining she was always "a ham".

"Now, you have to know her to know how she behaves normally to know whether this is deceptive or not."

Prof Wiseman thinks the faithful stars are going wrong by so far basing their assumptions on what people do and say, when "the best signals are what people don't say and don't do".

"Liars tend to be pretty quiet," he says, noting the difficulties of that with "a bunch of celebrities" who will be "used to being centre of attention".

Singer Burns, one of the traitors, told viewers she planned to "lay low" and go "under the radar", and it seems to be working so far.

Good liars also tend to be intelligent, Wiseman says, citing salespeople, politicians and - ahem - performers among those who will be "pretty high self-monitors".

"Alan Carr and Jonathan Ross are very used to interviewing people," he says. "And used to interviewees who will be somewhat elusive."

On the latest episode, beloved veteran actress Celia Imrie was seen telling her fellow participants: "People think I'm nice, but I'm not."

For clinical and forensic psychologist Dr Susan Young, the celebrity edition of the show adds an extra level of deception and intrigue due to the professional "impression management" of pre-existing personas.

Viewers "project pre-existing beliefs" on to the stars because "these are people who we feel we know", she tells us. But in reality we "can't tell where the performance ends and where it begins".

As "voyeurs of morality", she adds, "we can't wait for the nice person to do something unexpectedly".

The group dynamic is what interests Dr Young most because what lies beneath is an inherent "double bind". "Everyone must lie", she says, because "to be honest is dangerous"; and yet "lying corrodes the team", which is much-needed to complete tasks.

"What the show does here, it exposes the illusion of co-operation and that's in so many systems. It's in our workplaces, it's in politics, it's in friendships under stress," she says.

"At the end of the day, given certain circumstances and under certain pressures, altruism will thin and self-interest surfaces."

She adds: "It's almost like a social experiment, it's mirroring how quickly loyalty will collapse when incentives change."