Twenty-five years ago, the notion of a middle-aged Public Enemy appeared preposterous. Hip-hop's most militant group seemed defined by the inchoate rage of youth, the idealistic faith that a revolutionary restructuring of what they perceived as America's racist society could be willed into being by sheer righteous belief.

A generation on, they may be older and wiser but the fervent flame of anger has not dimmed. The names have changed but the story remains the same; where once Chuck D proselytised from the stage about Rodney King, tonight it is the modern morality tale of George Zimmerman and Trayvon Martin that exercises him.

Their miraculous achievement was always to make music as extreme, agitated and visceral as its radical lyrical content, and even today its serrated rage can shock. The aggregation of shrill sirens, deep-dub funk and testifying samples that make up Rebel Without a Pause still sounds astonishing, while the kinetic Don't Believe the Hype and Fight the Power are balls of tension, fingers jabbed hard into the solar plexus.

Professor Griff is absent tonight but, having missed Glastonbury due to "immigration issues", the antic Flavor Flav is back. Capering across stage, surfing through the crowd and dedicating a clenched Bring the Noise to the new King George (to a chorus of boos), he remains the perfect slapstick foil to Chuck D's magisterial ire.

The first half of the set, typified by Chuck D drawing links between 2012 track Hoover Music and recent revelations about American government surveillance, is taut and thrilling. The second hour, featuring Flav playing a drum solo and inviting women on stage to "shake their booty", is less so. Yet with hip-hop blighted by braggadocio and misogyny, Public Enemy remain a towering example of what it once was, and could be.

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