This week, the show’s New York publicists announced that Chicago has become the longest running production now playing on Broadway.

The story actually has a hidden subtext, since the reason that the 26-year-old run has taken the lead is the closure of previous star, The Phantom of the Opera. Given that the longest-running straight play on Broadway rarely stretches to more than a few months, Americans might struggle to understand how the two British leaders in the equivalent race until very recently were both straight plays.

By way of comparison, The Mousetrap has been running since just after the war, while The Woman in Black spent longer on stage in London than Chicago (so far) and Phantom managed in New York. In addition, The Play That Goes Wrong has had far greater longevity in London than New York and seems set to run for many more years, if not decades.

Looking at these five shows and adding the incredibly successful Les Misérables into the mix might prove instructive for producers hoping to hit the jackpot by finding a show that can enrich them for decades.

There is one common theme that applies to all of these shows and, to date, just about anything else that hits the jackpot. That is an intriguing and often strong underlying plot or theme. Jukebox musicals are all well and good, but generally remain pretty empty, relying on song and dance to cover up storylines that are often laughable. Perhaps the pick of the bunch is Mamma Mia, with a cheesy but likeable book written by Catherine Johnson, an established playwright.

When it comes to musicals, relying on novels as a starting point seems to be a good idea, although Shakespeare’s plays have also proved fruitful, along with other theatrical works.

Taking a bunch of tunes and linking them together with a negligible story must then rely entirely on an audience that loves the music. In addition, we have recently learned that too often it also takes massive amounts of alcohol and the opportunity to sing along, at least until the bouncers or the police arrive.

The jokers in the pack are the straight plays. What is it that has made The Mousetrap so successful?

With all due respect to the late Dame Agatha Christie, the plot is intriguing but hardly deep, rather like her characters. In this case, like The Woman in Black and Shirley Valentine, which this week announced that it has recouped production costs in record time, the success relies as much on the business acumen of the producers as the plays themselves.

Shirley Valentine has the unique attraction of Sheridan Smith, which will explain many of the ticket sales, but, like the other two, relies on low production costs, stability and word-of-mouth.

Increasingly, we are seeing solo shows and two-handers taking over even large theatres, increasing the chances of generating profits. Long-running shows are also self-fulfilling. Once a producer or a theatre owner has a hit on his or her hands, there is very little reason to close. Set-up costs for a new show will always be high and the chances of failure even more so.

A nice, quiet success story will plough on making money without the need for much expenditure on new costumes or sets and, in many cases, a stable cast of solid stage actors without big TV or movie followings and a dedicated crew all delighted to have the work.

Productions running for years isn’t always good news for theatre-goers, since most would prefer to choose from a wider range of shows that they have never seen rather than finding many theatres blocked out by familiar favourites, however much they enjoyed them first time around.

Beyond those that have already hit a decade or more, it is fascinating to ponder on which might be the current show that is most likely to be running in 2050 on both sides of the Atlantic?

You have to guess that Hamilton is hot favourite. It may not tick the low production costs box but has a plot and production formula that are unbeatable. Beyond that, if Sheridan Smith can wow audiences into old age and doesn’t have better offers, perhaps Shirley Valentine could surprise us all?

The pandemic has changed the outlook for everyone in the theatre industry and it will be fascinating to see whether other long-running shows on either side of the Atlantic close as a result and, even more compellingly, empty theatres discover new shows that could last for generations.