The costume institute and its annual gala in May at the Metropolitan Museum of Art, New York (the Met), have become fixtures on the museum world’s map and calendar. Whether you delight in them or are bemused by the spectacle they provide, or indeed try and take no notice at all, they are hard to ignore. The alignment they represent between fashion history, contemporary celebrity and the gravitas of a major museum is immensely beneficial in terms of fundraising and profile.