To illustrate this point in the foyer of the theatre there is a large sign with changeable numerals recording the number of performances of The Mousetrap that have taken place (well over 28,000).
I know all this because I went to see the play a couple of days ago. It was at the St Martin's Theatre, The Mousetrap's home for decades, but it wasn't the normal St. Martin's production that I saw, but rather a unique and different version.
Because, you see, I've been writing stage plays myself for years now, and as a result I've met a lot of very talented people, including an actor called Jamie Hutchins.
And Jamie Hutchins is appearing in a new Mousetrap production which is going on a tour of India this month (November 2019).
His company have been using the St Martin's Theatre for rehearsals. And this Friday they had a full dress rehearsal there — virtually indistinguishable from a full scale, finished production.
They invited an audience along to watch them perform. And I was lucky enough to be part of that audience.
Which meant not only did we get to see a beautifully polished performance of this classic thriller, in the best seats in the house — we also had the privilege of a backstage tour afterwards...
We saw the fly tower with its mechanism for sending down a steady cascade of styrofoam pellets, to simulate snow falling outside a window with startling accuracy.
We saw the small room where actors had more of these styrofoam pellets scattered on their costumes, so they could make an entrance as if racing into the sanctuary of Monkswell* Manor guest house from a fierce blizzard.
We saw the long table with painted squares for each vital prop to reside in, ready to be deployed, like the newspaper reporting the murder which sets the story in motion.
(There is also a gun, which is an especially crucial prop, and that has a place all its own, ready to be grabbed by the killer before they come on stage for the climax.)
And there was also this big, odd looking apparatus consisting of a cylinder of canvas lying on its side with a handle on it. When you turn it, it creates the whooshing sound of the eerie wind that persists throughout the play.
One of our party (not me) reached out to crank that handle, causing a stage technician to come running and intervene. "If you turn it the wrong way, all the damned canvas unwinds."
But we didn't just go backstage but also on stage. It was an extraordinary feeling to be standing in the set where the drama had just taken place, looking out at the seats of the theatre, past the dazzle of the lights.
On the mantelpiece of the set there's a clock which, like that canvas wind machine, has been doing service in this play since the very first performance. Thinking about the history associated with these objects is almost dizzying.
It was an extraordinary privilege to see this great play so beautifully performed, and then to cross over from the audience's point of view to that of the actors'.
On my way home on a dark, damp autumn evening, walking down grey pavements strewn with yellow leaves, I paused by the statue of Agatha Christie on Cranbourn Street and silently thanked her.
(Thanks too to Jamie, for making this happen. He is seen here (in the leather jacket) with me and his charming girlfriend Meena Begum on the set. My gratitude also to the multifariously gifted Conrad Blakemore for taking these photos. The other images are scans of the St Martin's Theatre flyer and a photograph of the Agatha Christie memorial, sculpted by Ben Twiston-Davies, taken from Bronze Age London. *The misspelling on the guest house sign is deliberate, a bit of comic business in the play.)