Last month, the American producers of Harry Potter and the Cursed Child were in boastful mood and with strong justification. Having now played for just over 1,800 performances, it is the fifth longest running play in Broadway history. We need to be careful of definitions here, since the word “play” leaves out musicals.

It is sad to record that, while the other four must have been incredibly popular at the time, they are now largely forgotten pages of theatrical history. For completists, the four plays that HP still has to conquer are Life with Father (1939–1947), Tobacco Road (1933–1941), Abie's Irish Rose (1922–1927), and Gemini (1977–1981).

In financial terms, Harry Potter and the Cursed Child is already top of the (non-musical) Broadway pops, having sold more than 2½ million tickets which have earned around one-third of a billion dollars in total sales. The statistics are quite staggering, and one hopes that the creative team behind the show are all still on a healthy percentage of the box office.

These achievements are even more impressive, given that Jack Thorne’s stage interpretation of J K Rowling’s young adult series that somehow managed to cross over into the adult market has no current competition.

Indeed, it appears to be the only Broadway straight play to have clocked up even 1,000 performances since the early 1980s, which was a bit of a heyday for the genre with Gemini supplemented by Deathtrap, Brighton Beach Memoirs, Torch Song Trilogy and Amadeus. Some might suggest that this is a sad indictment of audiences in the Big Apple and the producers who pander to them.

For those more steeped in the history of London Theatre, this news tells quite a different story. With all due respect to New York, many of us will struggle to comprehend the idea that no straight play has ever run for more than eight years on Broadway and only two have ever exceeded five years.

For whatever reason, Americans have always been less enthusiastic about non-musical plays, with periods not so long ago where they had practically disappeared without trace, if you ignored a handful of imports from across the Atlantic.

Readers may be interested to compare the US top five with UK counterparts, using the latest data from Wikipedia. The comparison is telling, when one benchmarks London’s finest to see how Harry Potter and the Cursed Child is doing. Even though it opened in London the best part of two years before New York and can therefore count around 800 more performances (counting Parts One and Two as a single performance), it is still years away from the top five.

It will not surprise anybody to discover that The Mousetrap is the granddaddy of them all. Still going strong at St Martin’s Theatre, the Agatha Christie whodunnit originally opened over 71 years ago and should be celebrating its 30,000th performance early next year.

The next five contain a few surprises but are considerably more familiar than their American equivalents. These are:

By monitoring these statistics, producers could learn a thing or two about the recipe for a long-running hits. The first lesson might be that it is almost impossible to find a show that will run for years.

Small-scale then seems to be the key, combined with sticking to comedy or thrillers. Indeed, if Harry Potter and the Cursed Child ever makes it on to the West End list, it will be bucking every trend of past history.