Tom Stoppard’s sense of the world being tugged between forces of frail enlightenment and powerful darkness finds disturbing expression in this perennially original black comedy for six actors and an orchestra: the first scene, in a miscast, spectacular production by Felix Barrett and Tom Morris, heralds the play’s abiding strangeness, its flair for provoking bleak laughter and for suggesting what it sounds like inside a madman’s mind.

Toby Jones’s agitated Ivanov, holed up in a mental hospital, hears music not voices. The real-life South Bank Sinfonia plays rear stage and its attractive music — composed by André Previn, often as pastiche Shostakovich — scales the heights of ineptitude to the patient’s hallucinating ears.

Every Good Boy Deserves Favour, premiered in 1977, poses a vital question for countries where the still small voice of dissent remains stifled.

What should you do if the price of leaving a psychiatric prison where you have been tortured for airing the truth about state repression, is to deny truth and confess that mania precipitated your allegations?

Stoppard’s original source of inspiration was the Russian dissident Viktor Fainberg, imprisoned and declared insane for protesting against the Soviet invasion of Czechoslovakia. He places just such a man — Joseph Millson’s poignantly anguished but steely Alexander, a haggard, shaven-headed victim of torture — in the next bed to Jones, whose misplaced performance turns Ivanov archly grotesque rather than pathetic and disturbed.

The lives of the two men, one unable to comprehend the truth, one pressured to deny it, run in comic, sardonic counterpoint.

The encounters between Alexander and Dan Stevens’s far too languid violin-playing “Doctor”, who seeks an excuse to release Alexander, are suffused with bitter, wonderfully absurdist comedy. “You are here because you have delusions that sane people are put in hospital,” Alexander is told. “Your disease is dissent.”

The interventions of Alexander’s young son, Sacha, who begs his father to win freedom by falsely admitting to madness, would have been more effective had not the directors weirdly cast a woman, Bryony Hannah, whose girlish winsomeness outrages conviction.

The orchestra’s sheer size lends airs of extravagant opulence to this unatmospheric production.Only the ironic finale,when a military colonel finds an excuse to free Alexander, an action which leaves this heroic protester still spiritually fettered, brings home the force of Stoppard’s rousing salvo for heroic dissenters in totalitarian regimes.
Until 25 February (020 7452 3000).