Tim Supple’s last Shakespearean production was The Comedy of Errors, a play with a farcical plot depending on the confusions caused by twins being mistaken for each other. Twelfth Night also famously involves a pair of twins, Viola and Sebastian, but this is a much richer, deeper play, more concerned with complexity of character than comic incident. Supple says:

“The twinning is important for what it allows to happen to people who meet them. But when they meet, it’s being brother and sister that matters.”

After Viola and Sebastian are separated in a shipwreck, each assuming the other lost, Viola dresses as a boy and seeks work in Duke Orsino’s household. The duke is in love with Olivia, who is in mourning for her brother. Her dissolute uncle, Toby Belch, is in residence and the household is ruled by the puritanical steward Malvolio.

Olivia falls in love with the disguised Viola while the duke also finds himself attracted to the “boy”, Caesario. All is resolved when Sebastian reappears to pair with Olivia, and Orsino can marry the restored Viola. Toby and his companions avenge themselves on spoilsport Malvolio.

A simple summary omits the contradictions and surprises. Supple believes the play is about changeability, and full of ambiguity and enigmatic behaviour. “We shouldn’t”, he says, “dislike Malvolio more than anybody else. He is self-deluding as all the characters are, given to arrogance and lack of generosity. It is helpful to see Malvolio, as Ted Hughes suggests, as Shakespeare’s first tragic character. Think of him as a prototype Macbeth.

“There is an important class element here - Malvolio is a faithful steward, but he is insecure and potentially vicious.”

Besides, Supple goes on, “Olivia’s household is a study in decay. Shakespeare is ambiguous about them all - Toby, Andrew, Olivia - they are all in a pit of decadence. There is a need for some sort of new Puritan thinking.” Olivia’s oath, to abjure life, is an expression of Puritanism, believes Supple. “Her journey is a release from the vow and a plunge into heady paganism.” Orsino’s court he sees as “more Catholic, more Renaissance, Italian, harking back to an Arcadian age”.

Viola and Sebastian are from another world. “Representing youth and innocence, they redefine gender and are a religious enigma.” Feste, Olivia’s Fool, is, says Supple, “probably the key to the play. He talks about pretending to be somebody else. He is a mirror to everybody else. A professional jester, he has feelings about the sadness and folly of Olivia.” (He uses logic to try to talk her out of her misery.) “He sees through disguises (except Viola’s) to people’s pretensions. Philosophically, he is a sceptic. There is a war going on for Olivia’s soul. With the Fool gone (he is dismissed for rowdiness) Malvolio isrunning the house - he has triumphed in death.”

At the start of the play, several people have had a brush with death. Maria, who invents the plot to humiliate Malvolio, “casts the spells. She, Toby and the others get possessed with their own trick. But she is a life force where others are preoccupied with death and decay.”

Heather Neill In rep until July 25. For details of performances and tickets tel: 0171 928 6363