Trans-global underground, Brixton Academy, London

Walking into this gig from the miserably wet south-London streets outside is like experiencing a violent change in the seasons: Manu Chao, his band and his crowd are a sunburst of exhilarating, positive energy unlike anything I've encountered in a while.

Chao, a diminutive French-Spanish 40-year-old, first found fame when, after his previous band, Mano Negro, split up during a tour of Colombia, he bought an old train and rode it deep into guerrilla country. Gathering up a strange cast of like-minded musicians and even circus performers, he brought his music of protest against poverty and injustice chugging into whatever town wanted to hear it. An instinctive nomad, turning up to strum for G8 protesters one week, forging links with anyone from Mexico's rebels of genius the Zapatistas to Europe's buskers the next, he has become an underground folk hero – and sold six million mostly Spanish-language albums along the way.

And this gig, far from the pointless, anaemic nature of much British music at the moment, seems an extension of that spirit. Though I'd lazily half-listened to Chao's last album, Proxima Estacion: Esperanza, put off by the language barrier, and though the songs tonight could be Marxist critiques or boy-band ballads for all I know, the communal rush of what Chao plays for two hours cannot be denied.

It starts with the band. One guitarist looks like a Gallic, Mohican-haired wrestler gone to seed, another like a kind-hearted skinhead; a tall, lithe, black singer trades songs with Chao, whose Barcelona football shirt is the only top on view. With an accordionist and trombonist, too, they look like a circus troupe as much as a band, like the talented misfits Chao met in Colombia.

The way they play, meanwhile, is physical and symbiotic: you can see energy building up like lava in the tensed body of the "wrestler", while the black singer, after an hour of leaping and exhortation, becomes languorous, letting others take the weight. The stage is generally a mass of jumping, sprinting but not chaotic bodies, but it's nothing compared with the crowd. With the lights full on them, so that everyone can see everyone else, they are an ocean of bouncing, waving arms, pushing themselves to the physical limit as much as the band, forming a loop of effort with the performers, each pushing the other on.

They are like a dream vision of Brixton, 4,500 people, drawn from every possible culture, having a grinning good time. The music they're listening to carries echoes of earlier periods, when such things occurred: the trombonist, particularly, recalls 2-Tone, while there are passages of Seventies reggae and punk. Except for Spanish-speakers, Chao's much-vaunted political spirit doesn't translate into anything specific. Instead, he enhances people's more beneficent, social notions by bringing them together in this way.