Somewhere beneath the skin and shock-absorbing layer of body fat of cult-film-turned-stage-musical Hairspray lurks a problem.

The story tells, of course, of teenager Tracy Turnblad – a girl The Who would have described as “meaty, beaty, big and bouncy”. Her ambition to appear as a dancer on her local TV pop show in 1962 Baltimore includes a growing determination to see the show racially integrated. The ridicule and aspersions Tracy receives because of her build give her common cause with the black kids. Yet while it is refreshing to see (as a programme essay notes) “a girl whose weight isn't the most important thing about her”, there is something too glib about, in effect, treating fat people as honorary blacks for the sake of a yarn.

The show is not just affirmative but passionate about racial equality; if Nina Simone were still alive, she would cover the second-act number “I Know Where I've Been”. But the fat business is treated as a bit of fun, and it plays calculatedly on what we will and will not consider grotesque. Leanne Jones' Tracy is not grotesque: although built for comfort rather than speed, she is some sizes more svelte than the young Ricki Lake in John Waters' original 1988 film.

Michael Ball as her mother Edna is grotesque because s/he is basically a pantomime dame in a fat suit (all those costume changes!), and moreover is filling the shoes of the late Divine, whose entire career was founded on bad taste. Of course, corpulent people are acceptable in entertainment, but you wouldn't want one of us living next door. Then, by association, the matter of racial equality is trivialised on the rebound: big dance number, healthy diet, end of problem.

However, in every other respect, this is one of those pesky shows that absolutely refuses to be disliked. Ball is terrific as Edna Turnblad; he relishes the “draggier” moments (the extravagant frocks, the sudden drop to basso for a word or two), but also knows how and when to – well, I hesitate to use the word “underplay” of a show like this. Jones, in her professional debut, deserves a prosperous career in more than just big-girl roles; she energetically sells Tracy's indefatigable good heart even when things are at their blackest. Making a now rare stage appearance as father Wilbur Turnblad, Mel Smith may need a bucket to carry a tune, but his and Ball's duet “Timeless To Me” is a masterclass in schlock.

Tracie Bennett turns in a gleeful performance as harridan Velma Von Tussle, the TV show's producer and the mother of Tracy's arch-enemy Amber. Johnnie Fiori as Motormouth Maybelle is commanding when she speaks and spine-tingling when she sings; in fact, this show with its custom-written pastiche numbers has more soul than the supposedly “authentic” but passionless Motown revue Dancing In The Streets.

I struggled hard to resist being washed away on the wave of feelgood this show generates but, in the end, washed away I was.