The premise of I'm With the Band is winning: part gig and part play, Tim Price's piece examines the fracturing of the British Union through the fracturing of soft-rock band The Union, the four members of which happen to be an Englishman, a Scotsman, a Welshman and a Northern Irishman. What sounds like the beginning of a bad joke does develop pleasantly, and the live music's a nice touch, but there's some difficult inconsistencies that make the lauded, sold out Edinburgh run hard to understand.

For starters, the allegory's very heavy – I can't quite shake the feeling that Price's characterisations are less born from human observation and more from trying to represent the different countries, and the very natural delivery just makes that distinction even more confused. However, despite the heavy-handedness, there are certain points where it seems to disappear: for example, Aaron's (the Northern-Irish one) relationship with Siobhan is clearly meant to be a reflection of the Troubles, but who on earth is Karen, Barry's (the Scottish one) girlfriend, meant to be?

Ignoring those, there's plenty to enjoy: the music is fun classic soft rock, with some nicely politicised lyrics, and the scenes in between have a lovely, natural energy, even if the characters have suffered as described above. The story doesn't really go anywhere, and ends with the almost ubiquitous physical altercation, but there's a classic rock-biopic inevitability to it that still makes for enjoyable watching.

But how has this gone from firm Edinburgh Fringe favourite to London without retaining whatever made it so popular up there? Arguably, playing to a quieter theatre after a sold-out run must be disheartening, and I'm sure there's something to be said for a large crowd making the show come to life more, but it feels like there's an element missing here that hasn't travelled.

I can't quite fathom it. Sure, Edinburgh (even the Traverse) sports a more rough and ready audience than London's culture vultures, or maybe the English just aren't as interested in the splitting up of the Union (arguably, they're the least affected), or maybe the lack of press attention because of the Edinburgh run – whatever it is, it's dampened the spirit of this production, and it's plain to see.

Nonetheless, it's not a complete disaster – the concept's refreshingly novel, the piece as a whole works, and it's a fun evening, if not the rip-roaring night you might have hoped for. There are enjoyably manic and energetic performances from all four actors (Matthew Bulgo, James Hillier, Declan Rodgers and Andy Clark), and plenty of jokes that will tickle anyone who's ever picked up an instrument; just don't expect to be blown away.

I'm With the Band, at St. James TheatreChris Hislop reviews I'm With the Band at the St. James Theatre.3