In so many ways is this disappointing Spice Girls tribute show a pale echo of Mamma Mia!: mother and daughter bonding, middle-aged love renewed, escape to exotic location (Spain this time), back catalogue dance-along, but with much thinner music than Abba’s.

Jennifer Saunders’ confused narrative - totally un-theatrical, completely un-satirical - lays down a girl group audition for a TV talent show, “Starmakers,” and suddenly lurches into something else: their sultry Posh lookalike, Viva (Hannah John-Kamen), is plucked for solo stardom and the rest fade into the background.

Viva, who lives on a houseboat with her foster mother Lauren (Sally Ann Triplett) is egged on by a vicious diva (Sally Dexter) who’s one of the judges, the Sharon Osbourne figure; there are also weak carbon copies of Simon Cowell and Cheryl Cole knocking about, but no chance of a proper send-up, let alone a timely critique.

For this is a damp, self-referential occasion, with Paul Garrington’s production – tremendous in the musical numbers; sound by Bobby Aitken, lighting by Howard Harrison, choreography by Lynne Page, all first-class – lacking the killer Mamma Mia! qualities of Catherine Johnson’s sly and witty book and Phyllida Lloyd’s ruthless direction.

Lightning hasn’t struck twice. One or two of the songs are well-structured but most are anaemic, until backroom boy Pablo whisks Viva to the vega and sings the title number with an acoustic guitar. But the Hispanic outburst, in overall dramatic terms, comes from nowhere. Like the Old Lady in Candide, we feel Spanish, suddenly Spanish. And there’s a cut-out black bull in a red silhouette.

Ben Cura & Hannah John-Kamen in Viva Forever!

Meanwhile, Mum is getting it on with Simon Slater’s tubby cab driver (“I had to get Joanna Lumley to Save an Elephant this morning”) to the music of “2 Become 1,” the closest Saunders comes to emulating Johnson’s trick of matching songs to the story.

Sally Dexter has a couple of extravagant moments, otherwise this is a musical theatre desert. I can’t even bear to suggest how feebly the “biological mother” strand is resolved. I may have imagined this, but at one point there are a crowd of illuminated pogo sticks on the stage, and then a poor, unrelated pun about Downton Abbey.

Several good issues are touched on and dropped like hot bricks: the sacking of “over-age” judges on television talent shows (Arlene Phillips was sitting in front of me), the grooming of talent for a homogenised culture, the need for friendship in a cut-throat career.

And there’s no explanation of the Spice Girls phenomenon that started with five singers, unknown to each other, answering an advert in a trade newspaper and forming a pop group that sold 75 million records and achieved nine UK number one singles.

Instead, the story of Viva is a non-story: she loves her mum and at the moment of her greatest triumph throws off her shoes (and her hair-piece) and cosies up with the mates she ditched on the way to the top. The plot they threw out the window in the first act never comes back. Instead, the hits roll out and the crowd goes crazy. Fair enough.