Textile designer brings florals, vines and smiley doodles to brand’s luxury checks for one-off paired collectionBurberry and Celia Birtwell are both national treasures of sorts. One is Britain’s grandest luxury name, the other the textile designer who dressed bohemian 1960s London in her prints and has a place in art history as David Hockney’s favourite muse.Burberry’s designer, Daniel Lee, has always loved Birtwell’s prints. When the two met this spring, he fell for “her energy, and