I have never seen a play quite like it. Yet Mike Leigh’s Ecstasy, like the best of his films, could not be more grounded in life’s realities. Revived at Hampstead Theatre where it first played three decades ago and now transferred to the West End, it demands from its audience and delivers in equal measure, bleak, seemingly interminable, but ultimately beautiful in its own way.

The year is 1979, the place a dingy bedsit off the Kilburn High Road, home to Brummie Jean, who is friends with Dawn, who is married to Mick, who is a former colleague of Len. Fuelled by cigarettes, alcohol and song, nothing about these four young people’s lives is notable, except their humanity, which Hampstead’s superb cast bring home with each verbal tic and physical stumble along the way.

Originally devised in the writer-director’s loose collaborative style, Ecstasy nevertheless largely observes Aristotlean unities of time, space and action. Or inaction. The most eventful things get is at the end of the brief first act, when the wife of a man whom Jean has been sleeping with breaks in and the room gets bashed up a bit. Even this only serves to set up the bottom-heavy second act, a post-pub drinking session that stretches long into the night and at the same time, into the histories and hinterlands of these (extra)ordinary characters.

Leigh’s unusual structure belies the mastery of his creation, asymmetrically bookended with two contrasting images of Jean (a remarkable performance from start to finish by Sian Brooke), lying on her bed with a man sitting near but distanced beside her. Leigh says his play is about loneliness and togetherness. What it shows, for good or ill, is that you can’t have one without the other.