The Ruling Class at Trafalgar Studios, London SW1

First performed in 1968, The Ruling Class was a savage and unprecedented assault on the venality of the upper orders and the Establishment at the time.

Theatre audiences loved it and its popularity was enhanced when it was adapted for the cinema, with Peter O’Toole taking the lead role of the 14th Earl of Gurney in the 1972 film.

In this well-staged and cast revival in the second Trafalgar Transformed season under Jamie Lloyd’s astute direction, screen heart-throb James McAvoy tackles the role of the earl with a demonic charm.

He succeeds to the title when his cross-dressing father (Paul Leonard, who carries off a tutu with great comic aplomb) perishes in an act of erotic auto-asphyxiation at the play’s attention-grabbing opening.

But it’s by no means a trouble-free succession — the 14th Earl, it turns out, is a paranoid-schizophrenic with delusions of godhead — and the plot revolves round his uncle and other family members seeking to get him sectioned so they can get their hands on the family loot.

As an actor, McAvoy’s blessed with great physical suppleness and he seizes all the comic possibilities the role offers as he prowls the stage, seemingly oblivious to the niceties of others’ “personal space.”

Emanating messianic zeal, he confounds the machinations of self-serving relatives, the church and the psychiatric profession as they attempt to rob him of his birthright.

By the play’s conclusion, his true nature as a murderous and misogynistic psychopath is revealed before he takes his place in a cobweb-encrusted House of Lords populated by peers in a state of terminal decomposition, where he delivers a bloodcurdling speech in favour of capital punishment.

It’s an ending entirely in keeping with Peter Barnes’s vision of an England where, Ukip-style, the hang ’em and flog ’em brigade rails against immigration and the “power” of the unions and where the rich man’s in his castle and the poor man’s still very much at his gate.

Barnes described the play as “an anti-boss drama for the shorn and not the shearers” and the former is wonderfully personified in the role of family manservant Daniel Tucker, who’s given a great comic performance by Anthony O’Donnell.

Throughout he acts as a splenetic court jester who, because he knows everything there is to know about the dark secrets in every corner of the ancestral pile, has free rein to shaft the devious machinations of his “superiors.” Somewhat improbably, he reveals himself to be a commie who all his life has been “working for the revolution.”

But his is a sole voice of resistance, eventually neutralised, and there’s no hint of a wider resistance to the perversions of ruling-class domination.

With the current Cabinet crammed full of Etonians and the second chamber still populated by characters who’d feel perfectly at ease in this production’s milieu, it was sobering to reflect at the play’s conclusion how little has changed since Barnes first lit the fuse on this devastating theatrical broadside.

And though the Trafalgar Studios are within spitting distance of the Palace of Westminster, there was no inkling of an insurrectionary charge along Whitehall from a well-heeled audience, who gave the show a somewhat muted response — McAvoy excepted — at the curtain call.