Something wicked this way comes

They deliver some of the most famous lines in Shakespeare yet they have no names. Their intervention sets in motion a terrible, blood-soaked tragedy. They open a play accounted so unlucky that many actors still won’t say its name under a theatre roof (they call it “the Scottish play”). But who are the witches in Macbeth? And how might they instil fear in a contemporary audience, for whom wafting about with cloaks and broomsticks is more likely to conjure Harry Potter than mortal terror?

The latest trio to tackle these vexed questions gather to talk to me not over a bubbling cauldron but in a bustling café in west London. Charlie Cameron, Anjana Vasan and Laura Elsworthy are playing the weird sisters in Kenneth Branagh's headlining production for the Manchester International Festival, which starts next week. None of them remotely matches descriptions in the play of bearded, withered hags and they won’t, they say laughing, be affixing pointy noises and warts. “I think just to play generic scary isn’t very scary,” says Cameron.

When Shakespeare wrote Macbeth witchcraft was a hot topic. King James I, recently ascended to the English throne, had participated in witch-hunts in Scotland and in 1597 had published a treatise on witchcraft, Daemonologie. Shakespeare and his audience would be well aware of the superstitions surrounding supposed witches and their association with the devil. In today’s more sceptical and secular age, the arrival of three wizened elderly women on stage might arouse more sympathy than fear. Yet they are essential to the dark power of the play and their first exchange, in the opening scene, sets the mood for a swift and horrifying descent into paranoia and slaughter.

Over the years, productions have sought ways to frame the eerie presence of these otherworldly beings. Some have found a setting where the presence of witches is not unthinkable. In 2004, Max Stafford-Clark’s version was set in a lawless African state where Macbeth encountered them at a voodoo ritual (Orson Welles’s 1936 version also drew on voodoo). Some have exploited conflicts between their appearance and their behaviour. A 1997 BBC television version, Macbeth on the Estate, channelled the classic horror movie idea of using children as vessels of evil, their smooth, expressionless faces contrasting with their apparently malevolent designs. Others have cast them as battlefield scavengers roaming a war-scarred landscape.

In Rupert Goold’s superb 2007 staging, the weird sisters were camouflaged as nurses who ministered to the soldiers on the battlefield, then secretly unplugged their life-support systems. It brilliantly foreshadowed Macbeth’s betrayal of trust: where there should have been care, there was murder. Gregory Doran simply deployed the power of darkness to get the skin prickling: his 1999 Royal Shakespeare Company production plunged the theatre into complete blackout for the witches’ first scene and later had them burst out unexpectedly from under a table, petrifying the audience.

In Manchester, the play will be staged in a deconsecrated church, a context that should add to the drama’s highly charged atmosphere. The company has been rehearsing in a church too, and co-director Rob Ashford says that the setting intensifies the play’s potent mix of the psychological and the metaphysical.

“You want to bring out the juxtaposition of good and evil,” says Ashford. “And how one profound moment can alter everything. Basically I think people are good until they’re evil. It’s about being tempted, hearing what you want to hear, allowing your ambition or jealousy to win over your good spirit, and just how scary and unbalanced the whole world is inside that situation.”

Rather than fight the ambivalence in 21st-century western society about religion and the supernatural, this production intends to use it. “There’s a sort of greyness in there,” says Ashford. “So we can play with the idea of the weird sisters’ power: how much power do they have or how much is the power of suggestion?”

This ambiguity is central to Macbeth. Crucial to the tragedy is the question of whether Macbeth would have become king had he not embarked on his murderous path. The weird sisters merely prophesy that he will be monarch – they don’t expand on how he might get there. It is what Macbeth chooses to do with that suggestion that drives the plot. Vasan says that she and her fellow weird sisters intend to emphasise the uncertainty about their role.

“We don’t stay as one thing throughout the play,” she says. “We inhabit a kind of in-between space and there’s always ambiguity. At some points we’re more human and at others more spirit-like, and we play with both of those worlds. What makes us powerful is being able to transform.”

“It’s interesting,” adds Elsworthy, “that we are described as all these awful things and yet they [Macbeth and Banquo] choose to believe us.”

It is that choice that unleashes the evil in Macbeth. The weird sisters don’t tell Macbeth to murder Duncan: they unlock in him a drive that is more powerful than his conscience. Perhaps this is what is most sinister about them: their ability to lay bare the human capacity for wickedness. Lucy Bailey, director of a 2010 production at Shakespeare’s Globe (where another new Macbeth opens this week), described them as the “gatekeepers to hell”: conduits to both the underworld and the internal hell of Macbeth’s increasingly tormented mind. Ashford points out that, although they fix the first encounter with Macbeth, he later seeks them out, like an addict.

In the Manchester Macbeth, the weird sisters are outsiders, pursuing their own logic. “As far as we are concerned, this is just what we are and what we do,” says Vasan.

It has been suggested that Shakespeare included the words from actual rituals in the witches’ spells, so bringing about the play’s notorious reputation for bad luck. Whatever the truth of that idea, the words they use are certainly disturbing: consider the potion they concoct, which is composed of dismembered animal bodies: “eye of newt and toe of frog”. The play’s use of language is brilliant and chilling throughout: it is suffused in sinister imagery, studded with ominous references to night, blood and darkness.

“A lot of the power is in the text,” observes Elsworthy. “I’ve learnt to trust the text, rather than trying to be weird. What they are saying is scary, and what they are doing is scary. Witches aren’t something that we in this society are scared of, but just what they are saying is disturbing.”

Indeed, the three actors confess to feeling a little unsettled themselves by the intensity of the play.

“When we finish our bit we all come out and we’ll all be a bit shaky,” admits Cameron. “We’re weird sisters: it’s not something you can just turn on or off.”

‘Macbeth’, Manchester International Festival, July 5-21, big screen relay, July 20, www.mif.co.uk; ‘Macbeth’, Shakespeare’s Globe, London, to 13 Oct, www.shakespearesglobe.com