Rob Brydon has the audience in the palm of his hand from the moment he trudges onto the stage.

He's Dudley: unsuccessful photographer, jilted husband and man on the edge. He’s checked into a London hotel in the hope of reconciling with his wife, who’s run-off with a Harley Street psychiatrist. When she refuses him, Dudley decides suicide is the only answer.

Written down, the plot of this 1969 French play sounds pretty bleak. In the hands of adaptor and director Sean Foley, it’s still bleak but it’s also extremely funny because every sorry line is punctuated by a pratfall or comic misunderstanding.

In the room next door is Kenneth Branagh, who plays a paid assassin. At first, his performance seems a bit straight compared to Brydon’s melodramatic anguish. Then his would-be killer is accidentally injected with horse tranquiliser meant for Dudley, and he starts tripping.

This is Branagh as you’ve never seen him before. He gurns, he crawls around on the floor mewling, he gyrates. One minute he’s mouthing off like an East End gangster, the next he’s doing a Russian accent while dribbling onto the bedspread. Not to be outdone, Brydon strips down to his undies and treats the audience to the sight of his jiggling pecs.

Their horseplay is slickly choreographed but farce is an acquired taste – an old-fashioned taste. Despite a newish translation, Francis Veber's play does feel a bit dated, especially the mincing hotel porter (Mark Hadfield) who’s agog when he walks in on his guests having sex, or so he believes.

Still, it’s a lot of fun – and when else are you going to see Kenneth Branagh on ketamine?