This shop has the last word in costume jewelry from the 1920s and onward. Chanel and Schiaparelli are just two of the famous designers that you might leap on here. And if you're lucky, you may find a piece that's been signed by its creator. These pieces are sometimes cheaper than those of the top-notch jewelers, and they may be of extra interest because you know who made them. Tube: Sloane Sq.