If it were any other show, the sight of the comedian Alan Carr sobbing under the burden of his dishonesty may have been enough to put off any celebrity thinking about accepting a place in the perilous Traitors’ castle.

Yet the second season of The Celebrity Traitors, being filmed at its now famous Highlands retreat, has managed to attract one of the most high-profile casts ever assembled for a reality TV show.

Actors who open West End shows and others with Oscar nominations to their name will be plotting alongside the nation’s most in-demand comedians and writers – and the odd fashion icon. The starry lineup was announced as filming began, amid speculation it would have been too hard to keep under wraps.

“I think it might be the most impressive lineup ever recruited for a reality show in the UK,” said Peter Fincham, a former BBC One controller and co-presenter of the Insiders: The TV Podcast.

“It seems to be full of people who, when you’re trying to cast a reality show with celebrities, you would normally say, ‘well we’ll never get them, they won’t do it’ … You can make phone calls you would otherwise be very nervous to make.”

The likes of Withnail and I’s Richard E Grant will compete along with Michael Sheen, who is about to star in a new theatre production of Amadeus. Jerry Hall may fancy her chances of spotting treacherous behaviour having survived her stint within the Murdoch empire.

The actor Bella Ramsey has agreed to enter the castle, alongside some of the most recognisable names in TV comedy including Miranda Hart, Romesh Ranganathan and James Acaster.

While celebrity appearances often come down to a cost-benefit analysis of how it will help their profile, Stephen Lambert, the chief executive of the show’s producer, Studio Lambert, said the reason most celebrities gave for signing up to Celebrity Traitors was the allure of the game itself.

“Almost without exception, the first reason is that they’re fans of the show,” he said. “Beyond that, the answers are surprisingly personal: people who feel they’ve spent their careers in a particular public lane and want to show a different side of themselves; people whose children or grandchildren have effectively dared them into it; people who are fascinated by the psychology of the game and want to see how they’d hold up under pressure.

“What we very rarely hear is anything to do with profile or promotion, which I think tells you something about the appeal of the format.”

Fiona Campbell, the BBC’s interim director of unscripted content, said producers had received some “surprising positive approaches” given the show’s popularity. “People will see their kids engaged in TV in a way they have not seen before and I think that adds an extra layer of ‘tell them I will give it a go’,” she said.

Apart from its runaway popularity, TV insiders pointed to the show’s other in-built advantages. Filming is intense, but not too long. Unlike other formats, there is no need to commit to hothouse training and there is no prospect of being asked to eat a kangaroo testicle.

Save for the actor Celia Imrie’s bout of flatulence in the first series, it also lacks the embarrassment factor. “It’s got everything going for it and I think that’s why it’s attracted an amazing cast,” said Fincham. “However big the celebrity, to say ‘I’m going on the Celebrity Traitors’, there’s no embarrassment.”

For those inside the pressurised world of celebrity booking, the fact that so many big names have signed up to be faithfuls and traitors should not take away the skill of the show’s casting.

“The amount of respect that people have for those who cast films over a TV show like this – it’s a million miles away,” said one seasoned TV talent executive. “But this is about casting. They’ve done an excellent job.

“It’s not just like a big list of famous people. You have to think about personalities. Somebody may be very famous, but they might not be very good on this. They might be a bit boring, or not willing to take risks, or not get stuck in, or not want to be with another group of people.”

Lambert concurs. “The perfect cast isn’t the most famous one, it’s the one where everyone brings something different to the table,” he said. “But yes, our brilliant casting director has many approaches from agents now everyone knows the show is so good.

“A cast made entirely of strategists would be dull, and a cast made entirely of big personalities would be exhausting. The magic is in the chemistry, and you can only really see that once the names are next to each other on the page.”

Insiders said on such big shows there was the added pressure of executives, producers and commissioners all having their own views on the lineup.

The fact that it is the spin-off’s second outing also helps. “You don’t have to sell them on the idea,” said a celebrity booker. “They’re sold.”

Some commentators have noted a skew this year towards actors, who understandably want to test their skills. The big surprise is the lack of athletes, given the breakout star of the first series was the rugby player Joe Marler.

TV insiders suggest a simple answer – Marler’s compelling demeanour and deadpan delivery are rare qualities in elite sport, a line of work that requires single-minded, monotonous dedication.

The writer Helen Lewis has also noted a glut of male comedians. As well as Acaster and Ranganathan, Rob Beckett and Joe Lycett also feature. “Have they no concerns about depleting Britain’s strategic reserves of male comedians so quickly?” she wrote.

Lambert says there has been no change to the show’s setting or conditions. “The celebrities have the same experience as the civilians taking part in the original version of the show,” he said. “One of the things the celebrities tell us they love is that the format strips everything back: the same accommodation, the same long days, the same lack of phones and outside contact for everyone. There’s a real democracy to it.”