A balmy summer's evening of jazz-funk should be an agreeable prospect, but Jamiroquai singer Jay Kay is not happy with the overcast skies. "I 'ate this fackin' country's weather," he rasps, in flawless estuary English. "Still, at least it's not pissing down, eh?" Resplendent in a three-foot-high Native American headdress, Kay is on robust form for his first UK gig in three years. His erratic run-ins with paparazzi may have made him a tabloid staple in recent years, but this ebullient dance festival headline set serves as a reminder that behind the playboy image is a meticulous musician at the very top of his game.

Ostensibly pushing their slick new studio album, Dynamite, Jamiroquai instead treat a well-lubricated Sunday-evening crowd to a greatest hits set. It's a seamless show, largely because they have rarely varied their sound during their 14-year career; Kay's musical influences run the gamut from 1970s funk to, well, 1970s funk.

This doesn't mean he's merely revisiting past glories. Recent single Feels Just Like It Should, an apparent ode to narcotic hedonism, is as good as anything Jamiroquai have ever produced, Kay's fetching falsetto cleverly riding the tune's fluid alchemy. Critical snobbery has rarely given him the credit he deserves as a vocalist.

Similarly, the lairy Kay may appear Essex Man incarnate, but a social awareness lurks beneath the constant smirk and preposterous headgear. An erudite inter-song address condemns the influence of "that Bush / Cheney / Rumsfeld crew" on the international arms trade, and sends hordes of apolitical clubbers scurrying across the field to the bar.

They come bounding back for material such as Cosmic Girl, Alright and an incendiary Virtual Insanity, before Kay ends the evening with a tetchy rant against the festival's 9pm curfew. Yet by now his set is into its third hour, and this particular funk odyssey has been quite long enough.