Big Ben is to chime non-stop for three minutes to help ring in the London 2012 Olympics.
Special permission had to be gained for the hour bell at the Palace of Westminster to be allowed to toll out of its regular sequence.
It will strike more than 42 times between 8.12am and 8.15am on July 27 to herald the beginning of the first day of Games.
It will be the first time Big Ben has been rung outside its regular schedule since February 15 1952, when it tolled every minute for 56 strokes from 9.30am for the funeral of King George VI.
The chiming for London 2012 will be a live performance as everything will have to be done by hand.
Mike McCann, Keeper of the Great Clock, said: "We need to manually lift the brake that controls the weight that drives the mechanism that strikes Big Ben."
The bells at the National Assembly for Wales, Stormont in Northern Ireland and the Scottish Parliament will also ring so that all four Parliaments will be chiming in unison at 8.12am, London 2012 said.
The event - titled All The Bells - will be the first big celebration to kick off the Games.
The idea is the brainchild of Turner Prize-winning artist and musician Martin Creed for the London 2012 Festival, who suggested all the bells in the country should be rung as loudly as possible for three minutes. He called it Work No 1197.
House of Commons Speaker John Bercow said: "It is a sign of how special this summer is when one of the world's most famous bells will ring outside its regular schedule so it can be part of this London 2012 Festival commission to ring in the Olympic Games."