So were we wrong? By “we” I mean the overnight critics, myself included, who gave largely negative reviews to the musical of Les Misérables when it opened at the Barbican in October 1985. All the statistics suggest we misjudged popular taste. Since it began the show has been seen by more than 130 million people, has played in 57 countries and been sung in 22 different languages. Faced with such daunting figures, I am reminded of George Bernard Shaw’s comment when he was accused of damning a Parisian boulevard comedy that had been a huge popular hit: “Forty million Frenchmen,” said Shaw, “can’t be right.”

But, as Les Mis celebrates its 40th birthday, it seems a good time to re-assess the show and ask why it has lasted so long. The first thing to say is that there is a vast difference between the show I saw at the Sondheim theatre last week and the one at the Barbican 40 years ago: the songs may be the same but the context has radically changed. When Les Mis opened it was jointly produced by the Royal Shakespeare Company and Cameron Mackintosh and was judged as a company product as much as a commercial musical. Re-reading the original reviews, almost all of them invoke Nicholas Nickleby which was produced by the RSC, directed by Trevor Nunn and John Caird and designed by John Napier. The big difference is that Nickleby was a two-part, seven-hour show that reflected the whole of Dickens’s novel; Les Mis was inevitably a drastic reduction of a 1,300-page epic and was viewed as much from a literary as a musical standpoint.

Even the show itself is not the same as the one I originally saw. That ran for three and a half hours. It now comes in at under three. Cameron Mackintosh tells me that cuts were made from the start when the production moved to the West End and then to Broadway in accordance with the overtime rules of successive musicians’ unions. Even more to the point, the production at the Sondheim is totally different from the one I saw at the Barbican. The new one is the work of Laurence Connor and James Powell but the really big changes are in the design and lighting. John Napier’s original sets were architectural: Matt Kinley’s designs are pictorial, rely on sombre projections inspired by Victor Hugo’s own paintings and even, in the labyrinthine sewers, reminded me of Piranesi. Paule Constable’s lighting is also extraordinary: at one point light filters vertically through imprisoning iron grilles, at others it comes in horizontal volleys to suggest the eternal pursuit of the ex-convict, Jean Valjean.

My original complaint was about the simplification of the novel’s moral dilemmas: never about the production. But this time round I worried less about the adaptation and was impressed by the hurtling speed of the staging and the shadowy beauty of the design. This still begs the big question of why a show loftily condemned by the critics, with the notable exceptions of Michael Coveney, Sheridan Morley and John Peter, is now celebrating its 40th birthday. One answer lies in the faith of its creators. Common sense dictated that Les Mis should close after its allotted eight-week run at the Barbican. Mackintosh, backed by Claude-Michel Schönberg and Alain Boublil (the show’s original begetters) and lyricist Herbert Kretzmer, decided otherwise, which is why Les Mis is still with us today.

Mackintosh has his own theories about the reasons for the show’s longevity. “It has much to do,” he says, “with youth. Hugo wrote mostly about young people fighting for their beliefs and a better world. New generations of young people are the mainstay of our audience as they rediscover Hugo’s timeless characters and have empathy with them. That’s why several of the key songs have become anthems of freedom and revolution around the world sung by people who have no idea these songs come from a musical.” Mackintosh adds that he “never imagined that schools with children as young as eight would perform the show as well as come to see it in a theatre. Because the show was put together by Trevor and John as an ensemble piece – with 32 actors playing nearly 300 roles – it has also become a training ground for every generation of young talent. What is fascinating is that most of the current cast were not even born when the show was first staged.”

I have my own theories as to why the show has outlived most of its original critics. VS Pritchett once wrote that Hugo’s genius was “for the creation of simple and recognisable myth” and what we get in the musical of Les Mis is a potent combination: the hope of redemption combined with the spectacle of poverty. The power of these two factors theatrically is confirmed by the two productions that sit alongside Les Mis in Shaftesbury Avenue. One is James Graham’s Punch which likewise celebrates the individual potential for spiritual re-birth. And Oliver! is about the fight for justice in a world of urban degradation.

In fact, there is an umbilical connection between Les Mis and Oliver! as Mackintosh explains: “It was while seeing my 1977 production of the Dickens musical and while listening to the Artful Dodger singing Consider Yourself that the character of the urchin, Gavroche, from Hugo’s novel popped into Alain Boublil’s head. By the end of the evening he had his next project. So I was always destined to be the midwife!”

I would offer yet another explanation for the survival of Les Mis: it offers audiences the kind of emotional kick that you normally associate with opera. There is a classic example at the end of Act One when a disparate range of characters – the persecuted Valjean, the policeman Javert, political insurrectionaries and ardent lovers – join forces to sing, from their different perspectives, One Day More. It is a powerful moment that sends the audience out for the interval on a high.

I still think there are things that get lost in turning the novel into a musical and I doubt that many people know what is really going on in the re-creation of the 1832 uprising. But seeing Les Mis for a second time was a chastening experience and one that reminded me that there are two things that audiences crave in the theatre and that are all too rarely found: an optimistic philosophy and a direct appeal to the heart.

• Les Misérables is booking at the Sondheim theatre, London, until 3 October 2026