EXTENDED REVIEW: The Boy in the Dress is a dazzling delight on the Stratford stage

Phew. Ever since the RSC announced that this year's Christmas show was to be a musical version of David Walliams' The Boy in the Dress with songs by Robbie Williams, it has been accompanied by a sense of everything from hope to desperation. Few productions at Stratford have been promoted more extensively; for the first time in my experience, the company has forbidden the publication of reviews until an appointed time, presumably to aid with a PR blitz coinciding with the visit of Walliams and Williams to the theatre. There is the feeling that the RSC not only wants this to be a gargantuan hit, but requires it to be: its previous successes include Matilda The Musical and a little thing called Les Misérables. What it would give for another.

So as wild applause and yells of delight rained down on the stage at the show's end, there will have been a good deal of relief mingled with the exhilaration. It turns out The Boy in the Dress is every bit as good as it needs to be, and probably a whole lot better.

Walliams' story follows Dennis, a 12-year-old with a fondness for football, fashion and a girl named Lisa James. Imaginative, original and emotionally astute, he feels different from the washed-out blandness and uniformity of his surroundings. His interest in clothes, his memory of his departed mother and the encouragement of Lisa lead him to try on a dress. Before long, life changes for Dennis, his family and his school. It's an enjoyably simple yet nuanced tale.

That this production reaches great heights is all the more impressive given how dreadfully it begins. The opening number is a song called Ordinary, and smug disdain drips from its every line as it mocks people who have the temerity to be - shudder! - lower middle-class. In their nondescript Estuary accents, a couple sing of how they shop in Lidl; someone tells of the fact that their father is a plumber; someone else "went to London once and found it scary". Worst of all, they all - wait for it - vote Tory. It encapsulates all that is worst about the RSC: for all its well-intentioned talk of inclusion, and for all of its efforts on matters such as race, gender and disability, there are far too many instances of rich people laughing at poorer people. Those who remember Little Britain will know that Walliams too has form on this front.

Mercifully, the show soon stops digging this hole and finds its heart. The set itself exudes charm, Quentin Blake's illustrations leaping from the pages of the book and finding three-dimensional form in all their scratchy glory, with exaggerated perspectives and smudgy colours. Dennis's skills as a striker are demonstrated in an artfully staged football match early on, quickly establishing the production's ruggedly balletic style, while the scraggly dog Oddbod, puppeteered skilfully, is a sweet and loving presence. Early fears that this might be one long, lavish sneer of a show were blessedly dispelled.

And then it really takes off with what might be the three best songs Williams and co-writer Guy Chambers have crafted. The first of these, A House Without a Mum, is quietly devastating, as Dennis, his dad and brother sing of the pleasures of being able to do what they want without anyone around to nag them. The immense sadness beneath the superficial jauntiness is quite heartbreaking; a few sobs and sniffles echoed around the auditorium. Is There Anything More Beautiful Than Lisa James? is sharp, fresh and fun; Williams' wit, which could grow rather wearing on record, feels quite at home here. And Disco Symphony is an all-out showstopper of epic proportions, accompanied by a dance routine of such sheer dazzling spectacle that the whole thing becomes almost overwhelming. This a show that does small beautifully and big brilliantly.

The second half rides on the waves of goodwill generated by the first. Beach Holiday Sunday returns us to the sadness and regret that lies at the core of the story and makes its positivity all the more powerful. There is tenderness and laughter and melancholy and fun and pain and triumph. When you're watching something this good, you just need to sit back and, as someone once nearly sang, let it entertain you. The resulting ovation was entirely deserved.

It would be a mistake however to conclude that the show is a guaranteed success based purely on its songs, staging and story. It relies heavily on the quality of its cast, all of whom were a credit to the RSC. Different youngsters perform on different nights; this night had Toby Mocrei as Dennis, and he excelled in his singing, comic timing, emotional depth and winning presence. Tabitha Knowles made for an endearing and warm Lisa James, with Ethan Dattani an assured Darvesh and Alfie Jukes suitably awkward as Dennis's older brother, John. Of the adults, Rufus Hound was arguably the stand-out performer as Dennis's dad, trying his best within his own limited parenting skills and finding his mind and heart broadened as the show unfurls. And while the creative talents of Walliams and Williams take top billing, Mark Ravenhill's script and Gregory Doran's direction bring out the best of their work.

There remains the nagging feeling though that, tremendous as this clearly is, its range and scope could be even greater. The final number is called Extraordinary and gives the appearance of addressing the problems of the first song, but fails to do so adequately. The scale of the show's compassion thus feels limited: there is no insight into the inner lives of all these supposedly 'ordinary' people, nor is there any examination of why habit and routine - derided here as mundane and parochial - may be attractive to them. The result potentially leaves audiences congratulating themselves on their open-mindedness and progressiveness while failing to examine their own prejudices. So while there can be no doubts as to the production's quality, there are perhaps questions regarding its true value as theatre.

But such qualms are likely to be swamped by the irresistible tide of joy the show unleashes. It would surely smash even the stoutest defences, winning over Williams-sceptics, Walliams-sceptics, whatever-sceptics. Far worse shows than The Boy in the Dress have sold out theatres around the world; there is no reason why this cannot be everything the RSC hopes it will be. Yet even if it fails in that regard, in can still be considered nothing other than a great success; for in a theatre in Stratford, on almost every night for the next three months, something amazing will happen. And that should be a source not just of relief, but of great pride, of a kind shown by this boy in a dress.

* The Boy in the Dress runs until March 8 2020. Visit www.rsc.org.uk/the-boy-in-the-dress-musical to book.