Big Ben is one of London's best-known landmarks, and looks most spectacular at night when the clock faces are illuminated. You even know when parliament is in session, because a light shines above the clock face.

The four dials of the clock are 23 feet square, the minute hand is 14 feet long and the figures are 2 feet high. Minutely regulated with a stack of coins placed on the huge pendulum, Big Ben is an excellent timekeeper, which has rarely stopped.

The name Big Ben actually refers not to the clock-tower itself, but to the thirteen ton bell hung within. The bell was named after the first commissioner of works, Sir Benjamin Hall.

This bell came originally from the old Palace of Westminster, it was given to the Dean of St. Paul's by William III. Before returning to Westminster to hang in its present home, it was refashioned in Whitechapel in 1858. The BBC first broadcast the chimes on the 31st December 1923 - there is a microphone in the turret connected to Broadcasting House.

During the second world war in 1941, an incendiary bomb destroyed the Commons chamber of the Houses of Parliament, but the clock tower remained intact and Big Ben continued to keep time and strike away the hours, its unique sound was broadcast to the nation and around the world, a welcome reassurance of hope to all who heard it.

There are even cells within the clock tower where Members of Parliament can be imprisoned for a breach of parliamentary privilege, though this is rare; the last recorded case was in 1880.

The tower is not open to the general public, but those with a "special interest" may arrange a visit to the top of the Clock Tower through their local.