Incidents in 2004 included a group of campaigners from Greenpeace scaling Big Ben's clock tower.

BBC: Parliament rooftop protest ends

People trust the Speaking Clock - Big Ben is timed by it.

BBC: Speaking Clock: Why are people still dialling for the time?

It is currently free to climb the 334 steps of the clock tower containing Big Ben.

BBC: U-turn over Big Ben trip charges

As a mark of respect, the chimes of Big Ben, as the bell and clock tower by the Palace of Westminster are commonly known, were silenced for the duration of the proceedings.

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The Mecca Clock Royal Tower Hotel, with more than 800 rooms, occupies what will soon be the world's second-tallest building, a structure incorporating the world's biggest clock, with faces at least six times the size of Big Ben's, and capped by a spire topped with a golden crescent.

ECONOMIST: A Saudi tower