At first Ian McKellen resembles one of those tsars who, even in modern times, believed themselves to be anointed by God and had little but scorn for the poor naked wretches whose desperation Shakespeare’s protagonist comes to acknowledge. At any rate, his Lear starts Trevor Nunn’s excellent Royal Shakespeare Company production by parading on stage dressed for some magnificent Orthodox ceremony, surrounded by obsequious Russian courtiers and radiating the arrogant complacency that ended the Romanov dynasty.

As Shakespeare’s play proceeds, Nunn’s latterday milieu doesn’t prove distracting. Indeed, it becomes obtrusive only when Lear’s knights roar in from the hunt to fire off rifles and do some obstreperous, Cossack-style dancing. But it makes an important point. This doddery ruler is cut off from people, children, reality and himself – and will make a journey more extreme and spiritually instructive than Nicholas II’s to that cellar in Yekaterinburg.

This is a superlative performance from McKellen that has lost nothing with its transfer from Stratford to London. Its centre is Lear’s question: “Is there any cause in nature that makes these hard hearts?” At the time the whitebearded king is putting a stool on trial in the belief that it’s his daughter Goneril. But McKellen delivers the line gently, quietly, and lingers over the word “hearts” in a wondering, interrogative way, as if belatedly discovering that such an organ exists – and exists in him.

Yet his isn’t a straightforward trek from hubris to enlightenment. It’s far more complex and complete than that. Always you’re aware of Lear’s contradictions. His opening love-test is a lark that abruptly turns hideously serious. He vows not to weep, then does so. He promises patience, then rages. His killer-threats are subverted by a breathlessness that signals cardiac trouble both real and spiritual. He laughs at the absurdity of things, yet feels them keenly, stripping to the buff in identification with Ben Meyjes’s raving, near-naked Edgar. He’s profoundly mad and deeply sane.

Above all, McKellen manages to exude vindictive fury while finding inside himself a concern, a care, a love that’s evident when he kisses Sylvester McCoy’s bumbling old Fool, or cradles William Gaunt’s sobbing Gloucester, or, now radiating a touching simplicity, is reconciled with Romola Garai’s sturdy Cordelia. And the scene with her corpse is hauntingly true, with Lear’s fatalistic repetitions of “never” resounding like muffled bells at a funeral.

Elsewhere, Monica Dolan’s Regan succumbs to drink and malice while Frances Barber’s smarmy-seeming Goneril makes a subtler journey, her animal self breaking through the defences that have kept her human and vulnerable. And meanwhile Christopher Oram’s set, reminiscent of the balcony of an old theatre, cracks and splinters – symbolising the mind, family, kingdom, planet and universe that Nunn’s revival is evoking so memorably.

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