You can get a behind-the-scenes glimpse of wealth and privilege, courtesy of the British government. The grand Hertford House near Oxford Street, once the home of the Marquess of Hertford, exhibits art treasures free of charge, from old Flemish Masters to Renaissance sculptures as well as collections of silver, porcelain and arms for which there is no equivalent anywhere else in the world. The café in the house’s conservatory is worth a visit after a morning spent shopping or touring galleries.