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

BBC: Parliament rooftop protest ends

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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