Big Ben: The Leaning Tower of London

Big Ben is making a big bend in the London skyline. According to documents recently published by Britain's Parliament, the neo-Gothic clock tower is gently leaning toward the northwest.

One of the world's most recognized landmarks, the 315-foot tower is slanting at an angle of .26 degrees. This is according to a 2009 report recently obtained by the Sunday Telegraph through a Freedom of Information request.

The documents show that the gilded spire atop the clock tower of the Houses of Parliament -- colloquially known as Big Ben after its massive bell -- is nearly 18 inches out of line, a measurement that can be observed by the naked eye, according to the report.

The tilt is now just about visible. You can see it if you stand on Parliament Square and look east, towards the river. I have heard tourists there taking photographs saying 'I don't think it is quite vertical' - and they are quite right, emeritus professor and senior research investigator at Imperial College, London, John Burland, told the Sunday Telegraph.

The lean was discovered when the Transport for London commissioned a report as it sought to extend the Jubilee Line under Parliament.

Experts remain uncertain what exactly is causing the tower to lean, but one theory is that the London clay on which the tower was built is drying out.

Mike McCann, who's official title is the Keeper of the Great Clock, has been monitoring the structure since 1999.

Our resident expert believes it will be between 4,000 and 10,000 years before it becomes a problem, McCann told BBC London. So it's not significant today, but we do need to keep an eye on it.

It is built on London clay and that can dry out and that can cause movement, McMann added.

To put it in perspective, the .26 degree angle is just one 16^th that of the Leaning Tower of Pisa.

There is no evidence to suggest that the lean was caused by work on the Underground, though a minuscule amount of movement was added to the natural shift of less than one millimeter per year.

The clock tower has been slightly off center since it was erected in the mid- 19^th century. Like many other buildings of its age, its position has shifted throughout the years due to several environmental factors such as seasonal temperature and moisture level changes.

The foundations for Big Ben were first laid in 1843 and the project was completed 16 years later in 1859, several years behind schedule.

Experts say that it would take thousands of years before the famous landmark and popular tourist attraction's tilt would become a serious problem.