The Houses of Parliament and the clock tower, commonly called Big Ben, are among London's most iconic landmarks.
The building is also known as the Palace of Westminster, and the clock tower is actually St Stephen's Tower.
Technically, Big Ben is the massive bell inside the clock tower, which weighs more than 13 tons (13,760 kg).
The clock tower looks spectacular at night when the four clock faces are illuminated.
A special light above the clock faces is also illuminated, letting the public know when parliament is in session.
Big Ben's timekeeping is strictly regulated by a stack of coins placed on the huge pendulum. Big Ben has rarely stopped. Even after a bomb destroyed the Commons chamber during the Second World War, the clock tower survived and Big Ben continued to strike the hours.
Clock Tower Tour / Visiting Big Ben in London
Tours are at set times of 9.15am, 11.15am and 2.15pm Monday - Friday with a max number of 16 people per tour.
Visitors to the Clock Tower will be shown up by a guide, who will outline the history of the tower, the bell and how the most accurate public clock in the world works.
Applications should be made in writing, as far in advance as possible, to:
House of Commons