Staff - which features modish swimwear by Chloé, Norma Kamali, Jil Sander and Tomas Maier, among others. They're hellishly expensive, of course (£173 for an emerald-green and teal-blue bikini with a cleverly skirted bottom, by Bronzette, a French label admired by Sofia Coppola); but undeniably chic.
Rather more affordable pieces are available at Boden and Toast, both reliable online sources for swimwear that manages to combine demure modesty with just enough sex appeal. I particularly like the latter's polka-dot bathing suits inspired by the 1950s - halter-neck plus lowish-cut legs - and the former's bikini shorts that can be mixed or matched with stripy tankini tops.