Every generation is accused of believing that it invented sex. In the wake of the Olympic summer, however, you couldn’t catch a tube without catching the eye of the blushing person opposite, precariously balancing Fifty Shades of Grey upon clenched knees. This generation’s late teens and twentysomethings might be forgiven for thinking their own, Jane Austen-style ‘coming out’ ball far racier than anything which had come before.