‘Write what you know’ has never been more apt. When a former Daily Express entertainment editor writes a play in which the showbiz section of his lightly fictionalized newsroom is called “Cunts’ Corner”, you know you’re in for a fun and filthy ride. Ruder about interfering proprietors than Drop the Dead Donkey, more racist and sexist than Malcolm Tucker in The Thick of It and just structurally shy of Richard Bean’s more smoothly-crafted Great Britain, Mark Jagasia’s Clarion is an uproarious debut and a stonkingly good cartoon of the dying and desperate days of ink-fingered journalism.