Rage Against the Machine, Finsbury Park, London

Last Christmas, nearly two decades after they started out in California, Rage Against the Machine found themselves at No. 1 in the charts as a result of a Facebook campaign to keep Simon Cowell's X-Factor contestants away from the top slot.

The cause may not be the most important one they have ever been involved in, but Rage cannot be accused of being ungracious in their response. To put on a free gig – sorry, "victory party" – is one thing; to hold it in Finsbury Park so thousands of fans can attend is quite another.

On screen a spoof animated Cowell introducing the band acts as a reminder as to why we are here, and comedy boos turn to cheers as an airhorn provides the cue for "Testify" and a surge towards the stage. Most bands like to pace their sets, but there is no chance of that happening tonight – there are no ballads or acoustic interludes, and each song seems to be greeted more rabidly than the last, although "Know Your Enemy" inspires a particularly crazed reaction.

Despite being reunited since 2007, there is no new material and the one surprise is a cover of The Clash's "White Riot". But although their last album of original material, The Battle of Los Angeles, was released over a decade ago, the music has aged well and the passion is still there. Zack de la Rocha prowls the stage, lecturing on Gaza and British music, while each song brings a new opportunity for Tom Morello to show what an innovative guitarist he is.

Amid the mayhem, the band bring on Jon and Tracy Morter, who started the Facebook campaign, and hand them a giant cheque for charity: "Fucking up the system never felt so good", says Morello. Before a triumphant "Killing in the Name", headlines and quotes from the chart battle flashing across the screen, the slogan "You Made History" appears. A cynic might say that the campaign's true legacy will be copycat attempts every Christmas rather than the destruction of manufactured pop, but that does not stop tonight feeling like a triumph.