Catherine Moss, who took journalists on a preanniversary tour, said that in one year as a Big Ben guide, she had climbed the height of Mount Everest three times over.
"It's my own private step machine," the trim-looking 51-year-old called down from the top of the tower.
No special events are planned, aside from an exhibition opening Sept. 19 in the nearby parliamentary offices.
Although the tan-colored tower above the Houses of Parliament is covered in gilt crowns, sculpted masonry, and coats of arms, the interior looks functional. The 14-foot-long minute hand casts a faint shadow over the pale white glass of the dial. The 5.6-ton clock mechanism, like a giant wristwatch, is wound three times a week. In the age of atomic clocks, its near-perfect time is regulated by heavy old pennies laid on or removed from the pendulum.
The chimes, supposedly based on four notes from Handel's "Messiah," ring out every quarter-hour from the intricately ornamented belfry. The bongs of Big Ben are heard every hour.
It is rare - and a matter of citywide consternation - for the clock to go mute. But wars and accidents happen. Initial construction was one disaster after another, and in 1916 the chimes were stopped for two years lest they guide German bomber zeppelins to the Parliament building.
Carried on BBC radio since 1924, the chimes took on added significance in World War II. Every night Britons observed a minute's silence as the clock struck nine. It was called the Big Ben Minute. Even as German bombs fell and air raid sirens howled, Big Ben's voice was heard.
The solemn chimes were a metaphor for Britons unflappable under fire, said Tam Dalyell, 76, a former lawmaker.
"It's defiant," Dalyell said in a telephone interview from his home in Scotland. "It's a sign of confidence and undaunted spirit."
On the night of May 10, 1941, an air raid wrecked the Parliament building, sending up flames as high as the belfry. A small explosive shattered the clock's south dial and damaged stonework, but the clock didn't skip a second.
