Plot: lan Yentob witnesses the birth of an idea at the hands of the designer, creator, and some call 'inventor' - Thomas Heatherwick - whose recent triumphs include the remarkable cauldron for the 2012 Olympic Games and the provocative redesign of the London double decker bus. Gaining a reputation as a maverick who defies commission briefs to come up with extraordinary creations - everything from dizzying chairs resembling oversized spinning tops, to a bridge that curls into a ball, and to the giant 'hairy' cube he built to represent Britain at the World Expo, Thomas is now incubating his most audacious plan for London yet