The Unfriend
Criterion Theatre | ★★★★✩

You know this comedy by Doctor Who writer and producer Steven Moffat is a genuine copper-bottomed farce when his hero Peter, played by the immensely watchable Reece Shearsmith, is standing in his suburban livingroom holding a toilet brush next to a visiting policeman who Peter suspects has been poisoned by his uninvited American house guest, Elsa (Frances Barber).

Until then the show, which was first seen at Chichester and is directed by Shearsmith’s fellow The League of Gentlemen star Mark Gatiss (also the director of Moffat’s Sherlock series), feels very much like a sitcom.

The action is set mostly in the living-room of a suburban house (all red brick walls on the outside and pastel banality within by designer Robert Jones) where Peter and his wife Debbie (Amanda Abbington) live with their surly teenage children Alex (Gabriel Howell) and Rosie (Maddie Holliday).

The plot also has an annoying nosy neighbour (Michael Simkins) who pops in a lot and whose presence is as unwanted as a hair in a gin and tonic.

Frances Barber as Elsa, Reece Shearsmith as Peter - photo by Manuel Harlan

Frances Barber as Elsa (Manuel Harlan)

However, Moffatt’s subject is not suburban life. He is much more interested in that thing which has happened to everyone who has ever been on holiday: finding that the pleasant friendship forged over polite conversation is in danger of becoming more permanent.

Only here he takes the problem a little further.

Elsa was good company when she and Peter were swapping banter about Trump while sitting on deckchairs during a cruise.

But just before she turns up uninvited to their home, Debbie has found out that their unwanted guest is a serial killer.

The laughs here are generated by the age-old clash between polite, feathery English etiquette and the bulldozer of brash Americanism.

When the English couple eventually pluck up the courage to confront Elsa about her family — many of whom have have died, according to a sensationalist American documentary called Killers At Large — the evening shifts up several gears.

What saves it from disappearing up its own stereotypes is that Elsa turns out to have a positive effect on the family. The dysfunctional teenagers not only become functional, but nice. In the role of the American widow Barber manages to be both sinister and good-hearted.

But the key here is Shearsmith, who conveys English repression like a pressure cooker about to pop. In another play it would not be altogether surprising if his Peter turned out to be a killer too.

Anyone seeking an antidote to our winter of discontent will be hard pushed to find a better morale booster than this.