Fashion Statement: Why we all appear to be heading in onesie direction Everyone's at it for winter. It's comforting, it keeps you warm, it's snuggly and it's nice. So why not go for it, in the privacy of our own homes? I'm talking about the ubiquitous trend for a onesie, of course - or for those less au fait with street parlance, an all-in-one. A jumpsuit. A catsuit. Actually a catsuit is a bit different, but it's still part of the all-in-one family. From boy-band One Direction and pop tadpole Justin Bieber, who both favour a man-made fleecy number in bright colours (looking for all the world like giant over-exposed children - oh wait, they are), to Prince William, whose RAF-issue onesie made an appearance in the papers last week (very practical - plenty of pockets but not quite enough space for HRH's, er, crown jewels), this unlikely item's allure is widespread, not just among sofa sartorialists but with fashion fans too. It all started four years ago when the jumpsuit returned from the wilderness - blame it on the Eighties revival, on the rise of minimalism perhaps, but suddenly this garment which had been nowhere was everywhere. Maybe it was something to do with the banking crisis and the impending feeling that we'd soon all be digging for victory and keeping our money in shoeboxes under our beds. We needed a garment that felt a bit "can-do." The onesie is the ultimate utilitarian piece of clothing, and it's just about the only concession to functionality that fashion is prepared to make. In recent seasons, where the emphasis has been on structure, minimalism and a certain wardrobe pragmatism, the onesie has really come into its own. The prevailing style has been military inspired, roughly tailored, often rendered luxurious by its finish - at Topshop Unique, in rich and sumptuous black velvet for autumn; khaki green at MaxMara in fluid, rippling parachute silk for spring (pictured above). The joy of a onesie is that, once it's on you're sorted. It's an outfit in itself, as chic as a dress but more comfortable - so you can look directional while making zero effort, which surely makes the all-in-one the holy grail of style. Perhaps there's more to Justin Bieber than first appears.