This is the play that established Caryl Churchill as the most imaginatively daring of our major dramatists; and, nearly 30 years after its premiere, it still seems not only remarkably inventive but as sharp about the contradictions of gender as anything that has been written since.

Consider Churchill’s first act and its cartoon treatment of the emotions she sees seething below the principled repressions of Victorian imperalism. The young adventurer she has seemingly modelled on Rider Haggard’s dashing Alan Quartermaine appears at a British outpost, where he adds the houseboy to conquests that include the district commissioner’s wife and young son, each of whom is played by a member of the opposite sex, and then makes an embarrassing pass at the commissioner himself.

The confusions of the African jungle itself can’t compare with those of an emotional jungle in which adultery, homosexuality both male and female, homophobia and every variety of intolerance and denial manage simultaneously to be rife.

With James Fleet exuding prim misogyny as the Queen’s representative, Bo Poraj nervily dimpling through the role of his wife, and others in topsy-turvy disarray, Thea Sharrock’s gripping production leaves you in no doubt of the gulf between moral pretension and visceral need. Likewise the second act, which involves the characters’ modern descendants, avoids caricaturing them but shows that the old problems haven’t vanished. People are less likely to judge or be judged, but they’re still unsure of their sexual identities, still floundering in their attempts to discover them, still unable to reach cloud nine.

Churchill emphasises this with one piece of cross-gender casting, which means that Fleet bounces hilariously about as a girl with a love of guns and smutty rhymes. But mostly the acting is realistic. Sophie Stanton is a lone mum and a lesbian who frees Joanna Scanlan from an unfulfilling marriage. Mark Letheren, the native servant in Act I, is now a promiscuous gay fretting against the wifely impulses of Poraj, whose mother leaves her own husband and rediscovers masturbation.

Can the intricacies of gender be summed up in terms such as “straight” and “gay” or even “man” and “woman”? Churchill’s suggestion, surely as provocative now as in 1979, is that this is to ask mercury to be as rigid as steel.

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