Before Julian Barratt and Noel Fielding have even taken to the stage, their audience erupts into the kind of roar normally reserved for rock bands and kings. At the end of their show, the first on a five-month tour of the British Isles, they leave to more muted hysteria. “Er, that’s the end,” says Fielding, stepping in front of a Morecambe and Wise-like red curtain as we sit there waiting for what’s next.

Well, the problem isn’t first-night nerves or the odd botched line – the Boosh’s conversational fantasia can easily absorb that kind of bother. It’s more that their show comes across as a bunch of half-formed ideas that have been patched together. Half variety show, half Mighty Boosh annual, it offers the characters the fans love – Bollo the gorilla, Naboo the shaman, the evil cockney hitcher – but doesn’t always know what to do with them.

Mind you, the sheer cheek of it sometimes outguns any silly worries about substance. They come on – the glitzy Fielding in a boat, the lowlier Barratt in a dinghy – to their electropop parody Future Sailors. They give Naboo and Bollo a hip-hop makeover, put down Honey Monster (“Yellow wanker!”), who “borrowed” their singing style for an advert, and give the geezerish octoped Harrison, played with relish by Fielding, his own chat show. It’s throwaway. But fun.

Their musical numbers, though, are a heavy presence. Fielding’s hitcher sings a song about eels, and it’s a set piece sorely in need of a storytelling context. Fielding and Barratt riff on their characters rather than drop many actual jokes. It’s trading on affection rather than building affection.

Worse, when they finally get going on a story in the second half, it’s a letdown. They perform a pseudo-earnest, ecological sci-fi play written by Barratt’s jazz-loving alter ego, Howard Moon, but it’s an undercooked version of an Ernie Wise play or something the League of Gentlemen’s Legz Akimbo theatre troupe might do. When Fielding’s not-very-altered-ego Vince Noir hijacks it, dressed like a Barbarella angel, and glams it all up, it perks up considerably. But compared with the undiminished creativity of their television work, this is thin stuff for £25 a ticket.

It’s day one, and performances will pep up, gags will come together, so perhaps we should cut it some slack. What may not change, though, is the structure, and it’s the wrong one for comedians who need narrative to keep them inventive rather than indulgent. There’s plenty to enjoy here: the energy of sidekicks, such as Rick Fulcher, who bursts out of his powder-blue safari suit; the casual chemistry between Barratt and Fielding; the inventive homemade aesthetic that still lingers. But likeable though it is, this is a show fit to maintain an empire, not to build one.

Touring. Next show tonight at the Pavilion Theatre, Glasgow (0141-332 1846). www.themightyboosh.com

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