Big Ben has a little bend.

Experts say the world-famous neogothic clock tower is listing gently, and documents recently published by Britain's Parliament show that the top of its gilded spire is about one-and-a-half feet out of line.

The tower -- colloquially known as Big Ben after its massive bell -- has been slightly off center since it was erected in the 19th century. Like many old buildings its position has been shifting imperceptibly for years as the ground beneath it subsides.

But a survey recently posted to the Internet shows that the clock tower underwent an unusual and so far unexplained shift of about 3 millimeters in 2003. One expert said the unevenness might now be just about visible to the naked eye.

"I have heard tourists there taking photographs saying 'I don't think it is quite vertical' -- and they are quite right," engineering expert John Burland was quoted as saying by the Sunday Telegraph, whose Freedom of Information request uncovered the survey.

Mike McCann, who's charged with looking after the tower's clockwork, shrugged off the problem, saying that such imperfections were a fact of life for older buildings.

"The Victorians didn't have lasers or modern surveying equipment," said McCann, whose official title is Keeper of the Great Clock. "It was never going to be straight to start with."

He put the degree of the tower's incline at about a third of a degree off the vertical, less than a tenth of the Leaning Tower of Pisa, whose tilt is world famous.

McCann said Big Ben's lean was "very, very minor," although he acknowledged that an eagle-eyed visitor might still be able to spot it.

"You'd have to be standing on absolutely flat ground, with your head completely straight," he said. "That's very difficult." 

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