THE MOUSETRAP features one of greatest secrets never told in modern Britain. No, not the detail of what Prince William was allegedly paid by a tabloid to settle a phone-hacking claimas trap-shut money by a tabloid. Or why there are more food banks in the country than there are McDonald’s food outlets.

No, it’s the perpetrator responsible for theatre’s greatest murder mystery, set in a play which has enticed audiences since The Mousetrap opened in London’s West End more than 70 years ago.

But why the attraction for this particular Agatha Christie tale, of a murder which takes place in a stately countryside guesthouse?

Why does seeing this play in particular make it onto so many lists of Things to Do Before I Die?

There are several reasons; the plot contains a greater twist than anything Chubby Checker ever sang about. Agatha Christie’s plot and character development is intricate and demanding of more brain cell gymnastics than a Herald crossword.

And the guests in the country manor, trapped together after being cut off from the world by heavy snow, are a fascinating bunch of potential malevolents, each with a compelling, often sordid back story.

When a police sergeant arrives, the guests learn that the killer is in their midst. But could it even be the sergeant himself? (A thought modern audiences will certainly consider).

And of course, there’s the complicity arrangement (keep schtum about the murderer) between the Mousetrap’s producers and audiences, which creates a sense of secret society. As a result, those who wish to know whodunnit have to turn up at the theatre.

But what the Mousetrap does so well is to evoke a sense of history. The play, based on a radio drama written to celebrate the 80th birthday of Queen Mary, wife of King George V, opened in 1952 starring Richard Attenborough.

It was a year when the last tram ran in London and when television programmes ended at 10.30pm. It was only seven years since Hitler had died, a world in which essential food was still rationed, Winston Churchill was Prime Minister and Elizabeth was beginning her long reign as Queen.

Yet, there is another reason why producers continue to entice new audiences to the showpiece.

A range of well-known actors are hired for the key roles, such as Todd Carty.

The East Londoner rose to fame in children’s series Grange Hill as Tucker Jenkins.

He starred as Mark Fowler in EastEnders (he made history by becoming the first mainstream British TV character to be diagnosed with HIV) and PC Gabriel Brent in The Bill.

Carty was also a contestant on Dancing on Ice, where he famously wobbled like a late-night drunk on a windy night in a cobbled street.

“I saw it about 40 years ago, when I was a much younger man,” the actor recalls of the play, “and when I got the call – ‘Would you like to be in The Mousetrap?’ – I didn’t hesitate.

“I remembered it being such a great play and I’ve always been an Agatha Christie fan, having first gotten hooked on her storytelling by seeing the Margaret Rutherford/Miss Marple films on TV.”

He adds: “Now, here I am 40 years later playing Major Metcalf in the UK and Ireland tour. It’s fantastic.”

Todd Carty is joined by Gwyneth Strong, who appeared as Cassandra in Only Fools and Horses, playing the force of nature who is Mrs Boyle.

“One of the things I really notice and admire from [Christie’s] body of work is that she is very good at writing interesting women. When you consider the time in which she was writing it’s quite fascinating. I think it’s boring to just see women portrayed in a very narrow prism.”

“I love Mrs Boyle’s anger,” adds Strong, smiling. “She’s very funny and bombastic. I wish I shared her confidence at being that angry but I’m the opposite. I bury any anger and let it out at all the wrong times. I really admire that she’s in the moment, she’s angry – and she’s not afraid to let you know it.”

The actor has managed to avoid screen death over the years. She’s survived Midsomer Murders, Murder in Suburbia and appearances in Silent Witness. So, stats for her survival of procedural drama suggest she should make it out of Monkswell Manor alive?

That’s not the way it works, is it?

“Well, of course, I can’t say!” laughs Strong. But what she will say is that when she first sat down to read the script she was captivated.

“I just got sucked in. I was supposed to be calling somebody and I thought, ‘Oh I’ll read the first half and call them back.’ I just kept on reading, reading, reading, and never called them.”

Gwyneth Strong says she didn’t feel any pressure in joining The Mousetrap, despite the play’s incredible success to date.

“Actually, I think because it is so well established it takes the pressure off.”

The Mousetrap, The King’s Theatre, Glasgow, May 1-6