Big Ben in London is leaning over and the tilt is now so pronounced it is clearly visible to the naked eye

It is believed the tilt is being caused by the 1858 landmark slowly sinking into the land on which it is built.

Decades of building work around the clock tower at the Palace of Westminster – including the extension of the Jubilee Line in the 90s – has weakened the foundations around the 315ft structure.

Recent measurements show the tower is leaning towards the northwest at an angle of 0.26 degrees, meaning the top of the tower is nearly one-and-a-half feet from vertical.

John Burland, emeritus professor and senior research investigator from Imperial College London who has worked on the Big Ben tower, said: ‘The tilt is now just about visible.

‘You can see it if you stand on Parliament Square and look east, towards the river.