Dear Lupin (Apollo Theatre)

At the moment, this potentially delightful two-hander for the cavalier Etonian racing correspondent Roger Mortimer and his wastrel Etonian odd job merchant son Charlie is a few fences short of a Grand National.

Father and son James and Jack Fox splutter their way through a frustrated but ultimately loving relationship, the one smooth and diffident, the other impulsive and awkwardly articulate, while director Philip Franks does his utmost to match the epistolary format to a bumpy dramaturgy devised by adaptor Michael Simkins.

There’s a bracing air of posh actor defiance about the show in the wake of criticism that working class lads and lasses are being squeezed out unfairly. Poppycock of course; I couldn’t see this brazenly upper class tract – the style of wit, and the style of life, strays somewhere between P G Wodehouse and Cold Comfort Farm – populated by the likes of Ray Winstone and Daniel Mays, for instance.

Posh purists may think it’s bad enough that a pair of Etonians is impersonated on the stage by the Harrovian Foxes, though the rest of us can’t really tell the difference. It’s the breath-taking, casual cruelty of dad’s remarks that give the letters such pungency, whether he’s fallen asleep and spilt his glass on his trousers, or the dog’s had diarrhoea, or – in the "not much news" category – three people roasted to death in a car accident at Theale.

Theale is near Newbury, and the slice of England we’re in is Berkshire and Hampshire borders where the rivers flow with gin and the horses define the social whirl. Dear Lupin, published in 2012, is a brilliant handbook of this segment of society, the name Lupin (for Charlie) borrowed from Mr Pooter’s disreputable son in The Diary of a Nobody.

Mortimer senior, who died in 1991, was in the Coldstream Guards, a prisoner of war and racing correspondent for the Sunday Times for 25 years, succeeded by Brough Scott who sat behind me (and Clare Balding) on opening night.

His borderline dodgy Jeremy Clarkson-style bulletins – "Yoko Ono is as erotic as a sack of dead ferrets" – are measured out between dollops of sympathetic affection, scraps of the theme tune from Grandstand (the BBC’s Saturday sports programme of yore) and, poignantly (he died aged 97 a few days ago), the live race commentaries of Peter O’Sullevan.

Quite apart from the feckless non-progress of Lupin through school, the Guards (nearly), experimental sexuality and rehab for drugs and alcohol, there’s a low rumbling ostinato of tight-lipped despair over Mrs Mortimer, known as Nidnod, whose cooking tastes of smelly plimsolls and whose drinking has gone beyond social: "Nidnod had her head in the bucket for a considerable period and was totally unplayable in the evening." When Lupin comes clean about not being so in rehab, dad asks, "Any chance of getting your mother in?"

Jack Fox is just starting out and James Fox has done very little theatre and it shows in both cases. There’s something forced and unpractised about their acting. But with a drastic overhaul and more playing in – though they have been on tour for some time, which is worrying – this could yet become a little gem of a show and a rallying cry for the politically incorrect, country life red trouser brigade, Etonian or otherwise.

Good to hear, too, an ugly come-uppance at one of Nidnod’s notorious dinners (more plimsolls) for Desmond Plummer, friend of the family, who, as leader of the old Greater London Council, was so unpleasantly censorious in the early days of the National Theatre on the South Bank.

Dear Lupin runs at the Apollo Theatre until 19 September. Click here for more information and to book tickets.