One of the biggest surprises about rock's response to the Iraq war is the silence from the rap community. Hip-hop is regularly held up as an attack upon every principle that America holds dear. However, its stars' protests have been low-key: Donald Rumsfeld is unlikely to lose much sleep over the news that Missy "Misdemeanour" Elliot and Jay-Z have signed an online petition.

The only major act to attack the war musically are veteran campaigners Public Enemy, whose furious Son of a Bush opens this show. The track has given Public Enemy a contemporaneity they have missed for a decade. A year after their definitive 1988 album It Takes a Nation of Millions to Hold Us Back, NWA emerged, shifting hip-hop's focus away from radical politics to trigger-happy nihilism. It has stayed there ever since. No one can deny Public Enemy's historical importance - It Takes a Nation's explosion of livid rhetoric and ear-ringing noise remains the genre's towering artistic achievement - but gangsta rap's success rendered them commercially obsolete.

The rise of George Bush, however, seems to have re-energised them. Tonight, the message behind a 15-year-old track such as Black Steel in the Hour of Chaos sounds surprisingly pertinent, and the music still astonishes.

Not everything about Public Enemy has aged well. Once hailed as a fearsome embodiment of black power, truncheon-wielding dance duo, the Security of the First World now seem strangely chi-chi. You would think twice about saying it to their faces - they are big blokes - but their synchronized routines could look no more camp if they performed them in glittery sailor suits to S Club 7's Reach for the Stars.

It scarcely matters when so much sense is set to music so shocking. Public Enemy remain one institution from hip-hop's golden age for whom nostalgia is not an option.