Getting to work on time

Tourists looked on in amazement yesterday as the specialist abseilers descended to one of the four clock faces, dangling 315ft (96m) in the air.

A third man, specialist heritage glazer Tony McGilbert, was then helped down to evaluate the necessary repairs.

The faces are set in a cast iron frame, 23ft (7m) in diameter, and there are a total of 312 pieces of opal glass.

But over time "capping pieces" which seal the gaps where the iron is bolted together can fall off, allowing water to get in and cause damage. And unfortunate fast-flying birds can also damage the glass.

Michael McCann, keeper of the Great Clock, said: "It might look risky but it's actually a very quick, convenient and safe way of doing it."