Don Juan in Soho rehashes an old Spanish yarn about a sexual glutton ruined by his appetite. Setting the story in modern London puts a strain on today’s play-goer, who tends to regard excessive promiscuity as a disease rather than a glamorous adventure. And the central character, a vulgar aristocrat named DJ who grades everyone on a scale of ‘fuckability’, contravenes the sentimental egalitarianism of our current sexual code.

Writer Patrick Marber offers us a version of London where the social structure of the Regency still endures. Educated Englishmen are the only fully evolved human beings. Beneath them swarms an amusing underclass of thick, greedy motormouths from whom the Englishman must recruit his prostitutes and servants. A lucky underling may, after prolonged contact with the Englishman, rise to membership of his circle on a semi-permanent basis. This is how Stan, (Adrian Scarborough) became the manservant of DJ (David Tennant). Scarborough is excellent, as always, but the role of buddy hardly stretches him. His portly physique persuades casting directors to see him as a bumbling clown but he has real substance on stage and a hard-to-read face with powerful hints of villainy. Iago is a role he could make his own. As for Tennant, he’s simply magical. He has some special access to the human heart whose sources are impossible to detect. Thanks to his extraordinary warmth and openness the seedy groper, DJ, becomes an amiable charlatan.

Suiting his performance to the script, Tennant gives a debonair, weightless reading, more a catwalk strut than a dramatic study, which gratifies and melts in the same instant, like a sliver of marzipan on the tongue. Marber’s script has lots of jokes, good and bad. Stan says his master’s libido is so overdeveloped that he would happily copulate with ‘the hole in the ozone layer’. But a character composed entirely of self-indulgence is bound to select language with the same failing. ‘I’m the Desmond Tutu of titillation,’ gloats DJ, ‘the Gandhi of the gang-bang.’ Alliteration apart, what facet of Gandhi suggests gang-bangs? And to associate Tutu with titillation is a flashy ingenuity without any wider resonance.

The plot concerns the aftermath of DJ’s divorce from a gullible teenager. The poor girl seems to have overlooked her beloved’s bed-hopping reputation and married him in the hope of finding romantic contentment with a man who gave up counting his conquests when the total exceeded 25,000. The girl’s brother, an armed thug, also mistook DJ for a pipe-and-slippers type and has vowed to slice open his throat. This barely credible back story creates suspense, of sorts, and leads to a bit of ketchup-letting in the closing scenes. But the tone of this slapdash play keeps shifting. There are comedy sketches, funky dances, farcical violence, nostalgic speeches about ‘old Soho’, and a stand-up rant aimed at talentless celebrities which Tennant mishandles, overdoing the anger at the expense of the comedy. Michael McIntyre might have done it better. A cautionary note. Tennant’s stardom originated in a family TV show but families should avoid this play because its emotional register is that of the boorish playboy crowing over his victims.

The Wipers Times by Ian Hislop and Nick Newman is about a group of soldiers at Ypres who started a newspaper with an abandoned printing machine. As a slice of history it works well. Etymological pedants like me will enjoy the linguistic revelations. ‘Mind your ps and qs’ and ‘getting the wrong end of the stick’ are both printing terms. The army slang sounds authentic too. ‘Fizz-bangs’ for incoming shells, ‘brass hats’ for officers at headquarters, and ‘na poo’, a corruption of the French, for ‘no more’. The odd solecism is noticeable. Would a British officer have said ‘not a problem’ in 1916?

There are constant gags about journalism, some of elderly vintage. An officer says he wants to create a newspaper ‘like Punch but with jokes’. The tone is unashamedly boyish and public-school. Offered cut-price sex at a brothel, an officer rushes back to the Front claiming that German shells are less scary than French hookers. And there’s no room for regular passion either. An officer on leave treats his wife to tea at the Ritz and their sexless conversation ends with her asking if he plans a return to the Front. ‘Of course,’ he says, as if the Great War were a career move offering marvellous opportunities for professional development. In the second half the play strays into less satisfying territory as the officers struggle against a booze crackdown led by a blousy prig claiming close friendship with Lloyd George. The action is interspersed with satirical excerpts from the Wipers Times re-written as comedy sketches. Though these are often funny, they disrupt the play’s rhythm and damage its claim to be a genuine drama.