The Great Bell, which resides inside one of the country's most famous and most photographed landmarks, first struck the hour on July 11 1859.

Although the nickname Big Ben is often used to describe the clock tower, the name was originally given to the bell itself

The origin of the name is thought to come from Sir Benjamin Hall, the First Commissioner of Works and Public Buildings, whose name is inscribed on the bell.

The anniversary will be marked with a night-time projection on the tower reading: "Happy Birthday Big Ben, 150 years, 1859 - 2009."

Mike McCann, Keeper of the Great Clock, said: "After 150 years, Big Ben still holds a special place in the hearts of Londoners and the world as a magnificent example of engineering and building genius."

Architect Charles Barry designed the new Palace of Westminster after a fire destroyed the old Houses of Parliament in 1834.

The clock tower was completed in 1859 and the clock first started on May 31 of that year, with the bell sounding for the first time just over a month later.

The first bell was cast in 1856 but cracked the following year under testing.

The second bell, weighing 13.7 tonnes, was cast on April 10 1858. It took 30 hours to winch into the belfry.

But its success was short-lived and in September 1859 it also cracked.

It was silent for four years until, in 1863, it was turned so the hammer struck a different spot.

A lighter hammer was also put to use and a small square cut in the bell to prevent the crack from spreading.

The clock tower stands 315ft tall, with each of the four dials measuring 23ft in diameter.

The original cast-iron minute hands proved too heavy and were replaced with 14 feet long copper hands which travel a distance equal to 118 miles every year.

The hour hands are 9ft long and are made of gun metal while 312 separate pieces of glass in each clock face.

Over the years the clock has been stopped accidentally on several occasions, by weather, workmen, breakages and birds.

In 1976 the Great Clock was shut down for a total of 26 days over nine months when part of the chiming mechanism disintegrated through metal fatigue.

Big Ben turns 150 years old in London