The work isn't finished on Big, if this stage musical of the beloved 1988 Tom Hanks film is ever to, um, make it big. A Broadway flop in 1996 where it was among the last shows directed by the late, much-admired Englishman Mike Ockrent, the material finds a sweetness in its West End incarnation that eluded it Stateside. But even with onetime boyband member Jay McGuiness adroitly capturing the manchild played by Hanks onscreen, the show remains awkwardly positioned between the satiric and the sentimental. And a ruthless pruning wouldn't go amiss either: by the time we'd got to the long-aborning finish, I was tempted to retitle the proceedings Long.
McGuiness in fact headlined a limited tour of this show three years ago, which has since been recast and retooled. No expense has been spared, or so it would seem, in a physical production that is busy without being particularly attractive. Simon Higlett's scenery, amplified by Ian William Galloway's place-setting projections, whoosh us from the Baskin family's Englewood, New Jersey home to the brash, bustling Manhattan where the newly 13-year-old Josh – an incipient teenager in a man's body – finds both a job and a girlfriend only to wish himself back to adolescence and to the comfort of, this being America, mom. 
Like the Oscar-nominated screenplay before it, the narrative here hinges on a lovely irony: by not having yet adopted an adult's wiles, Josh is soon endearing himself to one and all as "the real thing" when only he knows he is living a lie. Susan Lawrence (a strong-voiced Kimberley Walsh), the veep in charge of marketing at the toy manufacturing firm where Josh soon becomes (almost) everyone's favourite, exults in landing someone decent at last – even if her newfound date thinks spending the night means a "sleepover" and that Susan's job description has something to do with getting the groceries.
John Weidman's book is at its best when charting the unexpected bond that develops between these two. The romantically unlucky Susan is eager to show Josh off to her chums over a dinner party that comes to a (literally) crashing end, while Josh realises that females extend well beyond the elusive Cynthia Benson, the classmate on whom his younger self (Jamie O'Connor) is fixated at the show's start.
But when Big tries for attitude, it simply turns bizarre. That same dinner sequence comes with a peculiar quartet from the songwriting duo of David Shire and Richard Maltby that channels, of all things, the "Ascot Gavotte" from My Fair Lady, just as Josh's burgeoning relationship with the toy impresario, George MacMillan (a game Matthew Kelly, with the ensemble pictured above), puts one in mind of the similar employee-boss dynamic that helps drive How To Succeed in Business Without Really Trying. Like that 1961 Broadway classic, Big, too, positions a showstopper specifically around the effects of coffee, except that the one in How to Succeed is a lot better. (As for the ease with which Josh gets away with smashing up his host's $57,000 car, perhaps better not to go there.)
There's certainly a lot of score to Big, whose programme points to nearly 30 songs. Too many of them, alas, merely mark time or exist to give the kids in the ensemble an athletic workout in director Young's frenetic choreography. A second-act opener for Josh's best friend Billy (Jobe Hart, a genuine find all his own) is just one of too many numbers that feel like padding, so much so that the overkill then sells short a truly plaintive solo like "Stop Time", sung by Josh's adoring if anxious mother (Wendi Peters, above right). That role, too, seems contradictorily conceived. When first seen, Mrs Baskin is kvetching her way around the kitchen like such a scold that you aren't surprised when Josh seizes the opportunity provided by the fortune-telling funfair apparatus, Zoltar, to be big. And so Josh is transformed before our eyes.
Where this iteration really does, well, score is in the central performances from its two young stars, both of whom are veterans of Strictly Come Dancing and staked early renown on a media-friendly boy or girl band. Blessed with easily the best chops of the four named leads, Walsh fully delivers on Susan's defining self-realisation that she will never be able to retrieve her inner 13-year-old, as yet unaware that her adored Josh is 13 himself. And McGuiness, though far more comfortable dancing than singing, has the immediate likability and charm you can't learn at drama school. The unforced generosity of spirit he projects goes some way towards smoothing out an unsteady evening that, not for the first time, prompts one to wonder whether a littler, more streamlined Big might not be better.
