Discover what makes Big Ben tick...

The clock was designed in 1851 by Edmund Denison, a barrister and amateur horologist, and George Airy, the Astronomer Royal.

The mechanism, based on that of a grandfather clock, has remained unchanged since its installation and triggers the striking of the bells.

The clock is adjusted by adding or subtracting from a pile of pre-decimalisation pennies on the pendulum; each coin adds or subtracts a second.

Each dial contains 312 pieces of pot opal glass and is lit by 28 energy efficient 85-watt bulbs.

The 13.8-ton Great Bell was made at the Whitechapel Bell Foundry in the East End in 1858, using metal from an earlier 16-ton version made at Stockton-on-Tees, which had cracked during tests. Three furnaces were required to melt the metal.

The name Big Ben derives from either a large and ponderous MP of the time, Sir Benjamin Hall, then Chief Lord of the Woods and Forests, who spoke during the parliamentary debate on the naming of the bell, or a popular prize fighter, Benjamin Caunt.