Big Ben in London is leaning to such an extent that the tilt can now be seen with the naked eye.
A report commissioned by London Underground and the Parliamentary Estates Department says the 96-metre clock tower is sinking unevenly into the ground, causing it to lean towards the northwest.
The report says the level of the tilt has accelerated since 2003, increasing from 0.65mm per year to 0.9mm, but is not yet considered unsafe.
The main causes are years of underground rail developments and changes in ground conditions.
