More than 150 years old, it's the world's most famous clock - but with problems ranging from an aging mechanism and constant attack from pigeons, to surface-destroying pollutants and a weakening foundation, will England's Big Ben make it to the next century? Cared for by a handful of professionals, including metal workers, glazers, and three wise men who ensure the clock runs smoothly, it is a daily struggle to keep the clock upright and on time.