Chicken Soup With Barley, Royal Court Theatre

"Love comes now. You have to start with love," urges Sarah Kahn (Samantha Spiro) early in Chicken Soup With Barley, and it's inconceivable that Dominic Cooke's knockout production of Arnold Wesker's 1958 play could have sprung from any other starting point. There's talk later in Wesker's three acts (taken here with only one interval) of seeing people in the round, which is exactly what the writing, not to mention Cooke's superlative ensemble, manages to do: the political and the personal conjoined in a compassion that one might describe as clear-eyed if only it didn't prompt from an audience such honestly earned tears.

Wesker, 80 next year, was, astonishingly, only in his mid-twenties when he first penned a play that became part of his celebrated Trilogy, first seen at the Court in 1960. More than a half-century on, what compels attention isn't just the lament for the socialist dream as refracted through a working-class East End Jewish household where talk of "comrades", "pioneers" and communism goes hand in hand with the soup of the title - and countless cups of tea.

Even more blistering, at least in so empathic a take on the play, is the way in which a mother blazing with fervour and commitment and, yes, love attempts to connect to a landscape, public and private, that is seen across two decades to be severing ties with her. It isn't just that Mosley's fascists give way to World War Two and 1956 Hungary, allowing for a historical backdrop that never overwhelms the human beings centre stage. What's most striking is that Sarah's unbending tenacity to the cause seems foolish and wondrous, at once. No mere ideologue, she is seen crying out for beneficence in a world that has all but turned its back on her.

It helps that Wesker builds the play so artfully, his self-evident craft of a piece with a season in which the pleasures of the well-made play are reasserting themselves big time. In the first act, set in the Kahns' bustling household as crowds gather to face off against Mosley's blackshirts in the streets below, one is greeted with a panoply of politicisation, the International Brigade beckoning in Spain even as Sarah prepares to wage battle closer to home armed in the heat of the moment with a rolling pin. That's a kitchen utensil she might well be tempted to use on husband Harry (Danny Webb), a man so failure-prone that to leave him would seem a crime.

Come the second act, it's 1946, World War Two is over, and some of the Kahns are having second thoughts. Daughter Ada (Jenna Augen) dismisses "humanity" as high-minded claptrap and mocks her own mother for a solicitude that Ada views instead as so much egotism. Younger son Ronnie (Tom Rosenthal, making a dazzling professional debut) is impassioned, to be sure, not least about Beethoven's Egmont Overture and his own prospects as a poet, and there's a blissfully funny exchange when he explicates the joys of metaphor to his Aunt Cissie (Alexis Zegerman), who's more interested in the life of the trade unionist. And in quite literally reading the riot act.

The last act takes us to 1956, Sarah is nearly 60, and the weak-willed, once-loquacious Harry has been all but silenced by a series of strokes. And while politics and life exist as one for Sarah, others aren't so sure: not one-time firebrand Monty Blatt (Harry Peacock, in marvellously expansive form), who has settled instead for a quiet life with wife Bessie (Rebecca Gethins) and their unborn child. And certainly not Ronnie, who has returned from working as a cook in Paris beset by illness and soul-searing doubt.

"I don't see things in black and white any more," Ronnie remarks during one of the British theatre's defining climactic face-offs, the son all but forcing his adoring fusspot of a mum to leave the kettle to one side for once so the two can talk. But instead of achieving domestic détente, the play builds to a grievous schism that finds Sarah in isolated thrall to humankind, Wesker's conclusion its own cunning rewrite of the ending of Noël Coward's The Vortex. (Rattigan's The Deep Blue Sea gets a brief nod earlier on, as, elsewhere, do Chekhov, Tennessee Williams, and Clifford Odets.)

That the play resonates not just when voices are raised pays real tribute to Cooke, who finds a startling musicality in the shifts between cacophony and quiet, not least in the shift from the brouhaha in the street outside to the rancour that boils over within the Kahn residence. (Things change once Harry - who is younger than his wife - is sidelined by poor health, Sarah's task by that point turned from scold to caregiver.) Royal Court veteran Webb (pictured above in the character's banner-waving better days) charts Harry's decline keenly but without sentimentality, the damp patch on the seat of his trousers telling us all we need know about a physical disrepair that serves only to strengthen his wife's resolve.

As for Spiro's brilliantly realised Sarah, I suppose you could impute just a bit of Mother Courage to so pint-sized, pugnacious a figure in her refusal to be argued down from the fundamental decency she holds most dear. Let's just say that she cuts her own vivid path, culinary and otherwise, through upheavals that would have done a less galvanic personality in. You find yourself searching, as Sarah does, for love and light, even as darkness - in the act Wesker doesn't need to show us - eventually descends.