West London, the atrium of a tall, white building: two dancers rehearse a piece of modern choreography on a stage overlooked by four floors. Above them, giant papier-maché sardines swing on threads secured to a glass ceiling. Below, 30ft bamboo plants frame a sculpture of chrome and trickling water. This isn't a lottery funded arts centre or the head office of a global enterprise. It is the Chelsea and Westminster Hospital, the most spectacular in the NHS and where Cherie Booth is expected to give birth.