@ Festival Theatre, Edinburgh, until Sat 19 Mar 2016

Who is this Tom Jones worthy of a musical? The rambunctious Henry Fielding character made into a famous 1963 film by Tony Richardson? No, this is Jones, the Welsh pop singer whose unfashionable baritone made him an unlikely star in the 1960s. He emigrated to America with his childhood sweetheart, got pally with Elvis, became a live Las Vegas act, resurrected his career in the 1980s as sex symbol for the menopausal and, more recently, was a judge on BBC’s Saturday night shiny floor show The Voice.

It’s not exactly a biography of biblical proportions but jukebox musicals have been hung on a lot thinner material than this. Jones’s hits are memorable singalong ditties. His Delilah became a Welsh rugby anthem and was recently criticised for its tasteless lyrics (it’s about the murder of a prostitute). His Green, Green Grass of Home is a mournful, maudlin ballad that was the big hit of 1966. And It’s Not Unusual is an all-time karaoke favourite.

The producers and director Geinor Styles would do well to read the new book The Secret Life of the American Musical by Jack Viertel. The author delineates the key structural elements required in making a great musical – from “the second couple” to “the conditional love song”. Sadly Tom disobeys these rules and, frankly, comes a cropper. There’s a lot going for it – a likeable story of the hard nut from the Valleys who became a singing sensation, the love match with his wife,and songs sung with an impressive earthiness like the classic Long Tall Sally. There is some good writing from Mike James – “you could blow the bloody doors off with your voice” someone says, a reference to the line from The Italian Job – and some excellent observations about the not-so swinging 60s of “Welsh Wales”. The older audience members positively cooed in recognition when a top-of-the-line Silver Cross is wheeled on stage.

Kit Orton as Tom has the sideburns, swagger and Cuban heels – and the voice. He also has the strutting male sexuality rarely seen any more. At one point he is accused of singing and looking a truck driver. Yet as the story progresses there is too little indication of time passing and it’s difficult to know what year it is. When Tom goes solo and abandons his band, they unrealistically just shrug it off. The back projections can be worrisome: at one point, a huge spaceship seems to hover over the Welsh brick back-to-backs. But what really lets the show down is a criminally abrupt and crashing gear change when Jones finally makes it big and the story is abandoned in favour of a boogie with Tom’s greatest hits done in tribute-act mode. Dancing in the aisles is almost obligatory. None of this will deter what is a surely a dwindling number of the star’s fans.