Thanks to The Snowman and his Father Christmas stories, Raymond Briggs and Christmas go together like pork and chestnut. His magnificently gloomy 1977 comic book Fungus the Bogeyman is more of a stretch for a fun family show. But then who could have predicted that the muddy-toned tale of a big green Bogeyman having a midlife crisis would become a children’s classic anyway?

So the odds were against Marcus Romer, its adapter and director, who has had to inject more plot into Fungus’s trawl through the filthy tunnels of Bogeydom and the repulsive (to him) cleanliness of the “drycleaners” on the surface whom he has to scare and annoy.

Having jollied up its source material, though, this family show ends up without much personality of its own. Briggs’s storytelling is frugal but his world is vivid. Here, the familiar Briggs artwork of the show’s posters lures us to meet a slightly chubby onstage Fungus – plus wife Mildew and son Mould – in green facepaint and balaclava-style green headwear. It’s a notch above perfunctory.

The designer Ali Allen fares slightly better with the story’s two settings: downstage is Bogeydom, a raised upstage is the suburban Britain up to which father and son travel. But much of the action then takes place on a distant platform some 8ft above the stalls.

Still, there’s plenty of vitality from the cast, who play trombone (narrator Christian Edwards) or drums (Michael Lambourne as a gutsy Mould) and even a stinging guitar solo (Eamonn Fleming as a rather too amiable Fungus). “Bogeys love singing soft-rock power ballads,” says Edwards after the anthem We’re Bogeys and We Always Stick Together. But while Ivan Stott’s tunes are uncommonly strong, their mix of ska, Motown and disco is often foot-tapping yet rarely evocative of Bogeydom.

It’s pitched at children 4 and up, though some of the cultural in-jokes and fart gags – “How do you solve a problem like my rear?” asks Mildew (Joanna Swain) – will go down best with those a little older. My smuggled-in three-year-old liked the “lovely music” and was joking about slime at breakfast the next morning. But the humour is dealt with a cack hand, and there should be more audience participation sooner. Fungus does the job, just about. But he could do it with more charm.

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