In its fortieth birthday season, the Orange Tree commendably digs up an early play by its most remarkable “house” dramatist, Vaclav Havel, one written when he was a banned writer three years after the Soviet invasion of Czechoslovakia in 1968 put paid to the Prague Spring.

This is the British premiere – in a translation by Tomas Rychetsky and Carol Rocamara – of a play Havel says was the hardest to write, with the result that it may be his weakest; but Sam Waters’s spirited and perfectly cast production still makes of it a rousing political satire.

The former dictator is lying low. The makeshift authority resides with the head of the armed forces, the chief of police, the state prosecutor, the head of censorship and a rich widow who is an intimate, or at least confidante, of them all. Mindful of the dangers of “latent authoritarianism” this group forms a secret, revolutionary council.

Mayhem ensues to the accompaniment of the cries of tortured prisoners offstage, sullen protest on the streets, undercover sexual liaisons and hints that the senior judge might be a child molester. Havel’s point is that sexual depravity is a consequence of regime change corruption; the body politic is overrun with worms.

When the prosecutor’s wife finds him groping the office secretary, she makes him bend over and flays his bottom with his own belt. The chief of police sticks pins in any departing posterior. Helga the widow, played with lubricious malice by Lucy Tregear, keeps her top brass lovers dangling, until David Rintoul’s absolutely terrifying police chief seduces her in one of the most savage sex scenes imaginable.

The new committee moves towards dissolving parliament and silencing the media. But a surprise development stalls the headlong rush to the abyss. Or does it? This is a fascinating play partly because you never quite know where it’s going; and of course we’re obsessed anyway with what happens next in countries in turmoil.

The chief whip in these circumstances is not an officer, but a kid leather sex aid liberally applied by the police chief to his pliant and salacious widow. And the curtain line in the first act is just that: a reminder of a domestic shopping item.

It’s curtains in more ways than one for Christopher Ravenscroft’s furtive and oleaginous prosecutor, beset by Clare Vousden as his vinegary wife and various other weasel apparatchiks, deftly done by Kieron Jecchinis, Alister Cameron and Vincent Brimble. After a slow start, the black comedy accelerates with an irresistible momentum.