A committee of MPs is to investigate how to ensure Parliament's Clock Tower - better known as Big Ben - can be prevented from tilting further, after surveyors found it was leaning.
The Palace of Westminster, constructed during in the 19th Century, is also suffering from cracking.
The House of Commons Commission meets on Monday to discuss the problems.
But Professor John Burland of Imperial College said the lean should not be a big worry for at least "10,000 years".
During their meeting the MPs are expected to discuss a proposal to sell the Palace of Westminster and move into new offices, although this is thought to be highly unlikely to happen.
They will also look into the option of moving out temporarily while renovation work is carried out.'Long time ago'
The Clock Tower, housing the bell which is called Big Ben, was completed in 1859.
Since then a five-storey car park and the Jubilee underground line have been constructed.
Prof Burland, a construction expert who oversaw the building of the car park, told BBC Radio 4's Today programme the lean had "been there for years. When I first started work on the car park it was obvious that it was leaning.
"We made measurements on it. It was leaning at one in 250 to the vertical, which is just about visible. That's the break point between looking vertical and looking like a slight lean.
"We've known about it for years and it was probably developed at a very early stage because there's no cracking in the cladding and we think it probably leant while they were building it and before they put the cladding on.
"That was a long time ago and buildings do lean a little bit."
It is not the first time there have been problems with Big Ben, which stands at 96m (315ft) tall.
In 1976 pendulum weights fell down a shaft and the clock mechanism exploded, putting it out of action for almost nine months.
Prof Burland said the cracks in the Palace of Westminster had been there for years.
He added: "There's no such thing as an old building that isn't cracked. In fact they're beneficial because the building moves thermally more than is caused by the Jubilee Line and the movements concentrated around the cracks and, if they didn't, there'd be cracking elsewhere.
"So these have been there for years and they're certainly not caused by the Jubilee Line or the car park."
Although the tilt is nothing like as pronounced as that of the famous Leaning Tower of Pisa in Italy, it can still be spotted by the naked eye - just.
Prof Burland said: "If you stand in Parliament Square and look towards it, you can just see that it moves very slightly to the left, but I wouldn't put any political slant on that."
He added: "I calculated that it would take 10,000 years to reach the inclination of the Leaning Tower of Pisa. It's moving incredibly slowly and always has done so and there really is no immediate danger at all."
In its meeting the committee will discuss whether to set up a group to look into carrying out renovation work at Westminster.