An excellent brief documentary about a heroic grassroots political movement whose importance reveals itself more clearly in retrospect with every year that passes.

In late 1970s Britain, fascists and racists were gaining ground and members of the nervously silent political establishment were showing themselves the heirs of Neville Chamberlain and Paul von Hindenburg. A photographer and underground theatre activist called Red Saunders realised something had to be done. He co-founded Rock Against Racism to mount demonstrations and concerts against the far-right National Front and it was the great achievement of RAR to help to bring together the forces of punk, ska, reggae and the new wave – whose fanbases might otherwise be indifferent to each other – to present a united front to counter and mock the ugly bigots. This film confronts some uncomfortable truths: it wasn’t simply a matter of harnessing the innate progressive liberalism of pop music against prejudice.

Some of music’s biggest names (Clapton, Bowie, Rod Stewart) were making fatuous pro-Enoch Powell pronouncements – a bleary male-menopausal phase that can’t entirely be forgotten. And some punks were themselves displaying satirical shock-value Nazi emblems that we could have done without. Rock Against Racism channelled all that energy and rebellion, culminating in a glorious free concert in Victoria Park, east London – Britain’s Woodstock.

This film reminds you of the visceral power of the Clash and, indeed, the Tom Robinson Band. (Rubika Shah’s film also makes a spirited case for 999 being one of the best and most neglected punk bands.) Perhaps the most interesting case was Jimmy Pursey’s band Sham 69, which had a skinhead following. Sham 69’s appearance on the RAR bill was vital in reaching out to the white working class, who were ripe for NF recruitment. With racism now being becoming normalised in the corridors of power all over the developed world, the spirit of RAR is still needed.

• White Riot is in cinemas from 18 September.