Perhaps it’s her RSC work, but whatever the reason, the dramatic stars have aligned to create a performance of breath-taking authenticity and feeling

Deborah Warner’s fizzing, flawed – and brilliantly playful – take on King Lear contains a wink or a chuckle in almost every scene.

Bums are displayed proudly. Edmund skips to his soliloquies.

A raging storm is recreated with thundering sheets and blazing screens and, if you’re really lucky, Gloucester’s eye might fly clean past you. Atop these flourishes and twists – which are patchy but consistently sparky - there is a once-in-a-lifetime performance from Glenda Jackson as King Lear that will blow your mind and break your heart.

Perhaps it’s Jackson’s past as an MP (she only stood down from her Hampstead and Kilburn constituency in 2015) that makes her such a convincing politician in this modern-dress production.

Perhaps it’s her RSC work that makes her a singularly natural interpreter of Shakespeare. Perhaps it is her age (80 years) that allows her performance to shimmer on so many levels – both a testament to human resolve and a wrenching display of vulnerability. Whatever the reasons, the dramatic stars have aligned to create a performance of breath-taking authenticity and feeling.

Here is a plain-dressed King that is strong, sarcastic and a horrible show-off – with only a hint of the senility that will later take hold.

Jackson’s use of her hands is inspired: every flourish of the fingers deepens Shakespeare’s poetry. Most impressive are the moments when Lear curses ‘his’ daughters.

The rage that Jackson summons – the venom and heat that surges through her speech – is terrifying and otherworldly, as if Lear has finally made contact with God. The other actors sound a little clunky in Jackson’s presence. Harry Melling is particularly laboured as the wronged Edgar, and Jane Horrocks – as Lear’s false daughter Regan – feels awkward.

The comic turns work better and Rhys Ifans’ Fools is genuinely funny – no more so than when he has two eggs rammed in his eyes.

There are moments when this restless production flags and the screen-based set (Warner and Jean Kalman) is resolutely minimalist and ugly.

But despite a faltering second half, a dark tension builds as we wait – with dread and sick excitement – for Lear’s fate to befall him and for Jackson to return to the stage and tear our hearts in two.

Rating: 4/5 stars