There was a time when the biggest names in pop music believed they could change the world for the better. Faced with the intolerance and excesses of the established authorities, music celebrities decided to use their prestige to draw attention to the problems that less favoured people in the world faced. Wembley Stadium, London, 1988: thousands of English people fill one of the most famous football arenas in the world to celebrate an unforgettable pop music festival, with a lofty goal above entertainment - the celebration of the seventieth birthday of African leader Nelson Mandela.