There is an explosion in naturist holidays. It is estimated that 15 million people spent their holidays with nothing on last summer - four times as many as ten years ago. One tour operator predicts that naturist holidays will soon be as popular as ski-ing. At Cap d'Agde in the south of France a gigantic naturist town is being built. Already it has accommodation for 20,000. Soon it will be twice the size. And its supermarkets, banks, cafes and restaurants are full of naked people English families explain why they choose to go naked - many preferring the less commercial, back-to-nature resorts; few approving of the Mr and Miss Nude Admerica pageants staged every year by a Californian entrepreneur ' to bring nudism out of the closet and into the public eye '. JOHN PITMAN traces the growth of the naturist movement this century, from its small-time beginnings in a park in north Germany, to the multi-million-pound business it is today - especially for France and Yugoslavia.