On a sunny Thursday afternoon, the Covent Garden branch of Gong cha is doing a roaring trade. Staff behind the counter are busy preparing drinks for a string of customers, all ordering from an electronic pad in the corner. One leaves with a purple concoction flavoured with the root vegetable taro; another sips on a milky tea laced with brown sugar “pearls”. A third grabs a bright drink tasting of passion fruit and adorned with floating coconut jelly. It’s a scene being played out more and more as bubble tea shops like Gong cha pop up around the UK. Wisbech, Cambridgeshire, has just got its first (called Just Poppin); in Canterbury, Kent, there are six shops to choose from; and a new branch of American bubble tea brand CoCo recently had dozens of people queueing down Glasgow’s Bath Street. Alongside the specialists, high-street stalwarts are also turning their attention to the drink. After dipping its toe in the water last year, Costa Coffee has put three bubble tea frappés on its summer menu (in addition to the two more-conventional versions it sells under “iced teas”), while supermarkets have added DIY kits to their shelves. After decades of bubbling under the...