Chariots of Fire at Hampstead shows how amateurism in athletics, province of poshos at the older universities, was undermined by a Jewish immigrant, Harold Abrahams, hiring a professional coach, and the Americans beefing up - steroids are just around the corner - on the training circuit.
Interestingly, of course, Abrahams' chief adversary isn't a posh boy at all, but a committed Christian Scotsman who ruffles feathers by refusing to compete on a Sunday. These protagonist outsiders, however, are bathed in the refelected glow of the Establishment, with its antisemitic mutterings and snobberies, bunting and Gilbert and Sullivan, and rousing choruses of Rule Britannia.
Is it an accident, I wonder, that both Chariots of Fire and Posh arrive in town in good time for the Olympics in the Queen's diamond jubilee year? The official Olympic cultural programme may boast all sorts of European avant garde credentials, from Cate Blanchett in Botho Strauss, to Pina Bausch and Robert Wilson.
But Chariots and Posh are going to be far more resonant with the general British public. If they can be bothered about going out in the summer evenings, that is, and don't prefer to stay home glued to the television watching the sport itself - as well as the Test Matches and the European Championship in soccer.
I took a dim view of Chariots on Tuesday night, not because I disliked the show, but because I was watching it through my prescription sunglasses. In the joyous surprise at the outbreak of summer sunshine, I was popping in and out of the garden in the afternoon and, when I changed for the theatre, was still wearing the shades and forgot to add my regular specs to the first night ensemble.
So there I sat in my chunky wraparound Calvin Kleins, looking for all the world as though I'd a) joined the Mafia, or b) suddenly developed a serious eye infection, or c) arrived hot-foot from a David Gest lookalike competition.
The great advantage of theatre-in-the round, or traverse staging - and designer Miriam Buether's arena stadium is a bit of both - is that you feel so involved in the play. The great disadvantage is that you can see everyone else in the audience.
So there was no chance of hiding in the shades in my shades. I had to tough it out. Well, so did everyone else, to a greater or lesser extent. Especially two lonesome rows of first-nighters ranged in opposition to each other across the playing fields of Paris and Cambridge: on the one side, Adrian Lester, David Hare and Nicole Fahri; on the other, Alison Steadman, Rufus Norris and Patricia Hodge.
I wonder how the audiences will be for Posh. Michael Billington, in his Guardian review, suggests that the play will fare better in the West End with a more mixed audience than at Sloane Square. But the play packed out in Chelsea, probably because the very type of person whom the play satirises turned up in droves to have a jolly good laugh at themselves and cheer on the violence.
One thing's for sure. Unless they do something about the dodgy and often garbled articulation of the actors, the non-poshos at the back of the Duke of York's stalls will have only an imperfect grasp of the play's dialogue. And that would be a terrible shame.
People talk about a renewal of the class war, but the class war is a constant battle in British society. For all David Cameron's professions of care and compassion - and he really does seem a decent enough bloke - most people in this country know that he was a member of the Bullingdon Club whose disgusting behaviour is satirised in Posh, and that he is the fifth cousin, twice-removed, of the Queen, married to the daughter of a baronet, with a reported personal fortune in excess of £30m.
So he's one of Them, not one of Us. And that, for most people, for good or for bad, makes him an enemy of democracy and fair play. Nothing he can do about it, of course, but that's the way of the world. And that's what Posh is really about.