Big Ben is slowly turning into Britain's version of the Leaning Tower of Pisa, a survey has confirmed.
Tourists have spotted that the iconic landmark is no longer vertical, with Professor John Burland, of Imperial College London, admitting: 'I have heard tourists saying, "I don't think it is really vertical". They are quite right. The tilt is now just about visible. If it started greater acceleration we would have to do something in a few years.'
The Palace of Westminster's clock tower has, in fact, not been perfectly vertical for years following ground moving conditions and tunnelling for Tube lines.
Now engineers are warning that if the tilt is left untreated, the tower could topple over completely in many years to come.
The peak of the 315ft tower currently has a 0.26 degree tilt to the north west - one sixteenth of the Pisa's lean - leaving it 18 inches, or one-and-a-half-feet, off where it would be if it were vertical.
And a recent survey for the London Underground and Parliamentary Estates Department has found the rate of movement has increased in recent years, causing cracks to appear on the walls in the House of Commons.
Since 2003, the tilt has increased 0.04 of a degree every year. Experts reveal that at that rate it would crash into the Portcullis House - used as MPs' offices - in 5,000 years' time.
Big Ben is actually the nickname of the tower's largest bell, but the public and tourists generally use it as the name for the whole clock, which was built in 1853.