Nobody can quite believe that the Rolling Stones are playing their first rock festival for many decades, until the duelling guitars of Keef and Ronnie Wood circle around each other in the sweet night air, saxophones honk, and Mick dances like a moth in the flames. And other festival guests, notably a fragile looking Amy Winehouse, come up for a duet. But most amazing of all is when the stage sails off into the crowd with only Charlie Watts looking unperturbed, along tracks of steel erected overnight, and no-one misses a beat.