A holocaust happened in 19th century Congo. There were ten million victims and the perpetrator was Belgium, a country more often teased for being unremarkable than condemned for being an architect of atrocity.

Yet if Martin McDonagh’s new play was partly intended to throw light on a subject best known for Conrad’s Heart of Darkness it does so in a most obscure way.

Jim Broadbent hilariously plays not a Belgian but none other than Hans Christian Andersen, who is riding high on the success of children’s stories such as The Little Mermaid and The Ugly Duckling, all of which which we discover are actually written by a crippled Congolese pygmy woman called Marjory (Johnetta Eula’Mae Ackles) who Andersen keeps imprisoned in his Copenhagen attic.

Quite why the great Dane has been chosen as the bogeyman of European colonialism is never made clear. But McDonagh, Oscar-winning writer/director of Three Billboards Outside Ebbing, Missouri, whose recently revived Lieutenant of Inishmore makes Pinter’s attempts at stage violence look dated and coy, is apparently in urgent need of a metaphor.

This one — the pygmy in the attic — might suggest that, much like empires, great literary figures owe their success to exploiting something other than themselves. For when Andersen visits Dickens here, and hilariously confuses his host’s name with Charles Darwin’s, it turns out that the author of Bleak House also had a pygmy in his attic, and not in the way that some people have skeletons in their cupboard, but in the way that some actually have a wardrobe with bones in it.

Much of Matthew Dunster’s production is set in designer Anna Fleischle’s spooky vision of Andersen’s shadowy attic which is bedecked with hanging puppets. And with this mash-up of metaphor, satire and history you are not meant to know exactly where the lines separating these ingredients are drawn. But because it is all pitched as comedy — and is often very funny in the way it depicts two of Europe’s most esteemed literary figures to be potty-mouthed barbarians — you are invited to feel that it doesn’t much matter what is true and what is not. But it does matter, doesn’t it?

Granted, it’s all very entertaining and you leave having laughed a fair amount and with Tom Waits’s recorded narration ringing in your ears like a coffee grinder. Yet the sense of having witnessed an audacious piece of theatre is somewhat sullied by the smug satisfaction of a production that it is in on a joke that remains hilarious only to those in the know. And as McDonagh’s crude version of Dickens might say, f**** that.