The Tower of London is on the verge of being placed on the United Nation's Heritage in Danger List, Unesco has said.
The 900-year-old Tower was built by William the Conqueror
The UN's cultural organisation fears the 900-year-old Tower has become overshadowed by skyscrapers which are threatening its historical value.
New developments "appear not to respect" the tower's location, it said.
Experts are visiting the UK to assess threats to the tower and other sites like Liverpool's Waterfront.
They will also look at the Houses of Parliament and Westminster Abbey.
The Tower of London, built by William the Conqueror, is among 830 sites across the world which have been granted World Heritage Site status by Unesco.
In July, Unesco's World Heritage Committee said it was "concerned" that new developments were overshadowing heritage sites and that London's planning policies to protect the tower were not "applied effectively".
World Heritage Committee member Kishore Rao told BBC Radio 4's Today programme: "If you have modern buildings coming up all around it and people - pedestrians - can't view a certain historic building against the skyline or in relation to other historic buildings in the vicinity, then it loses the value.
"You don't only maintain the authenticity of the site - that means that the structure itself is not damaged or modified - but also that it is presented in its historical context."
Neville Shulman, a member of the UK Culture Committee for Unesco, said: "Once you lose the views, you start to lose the intrinsic value of the buildings and suddenly people start to think about demolishing, altering, changing in many different ways."
The leader of Liverpool City Council, Warren Bradley, said he had had positive discussions with the inspectors when they visited the city this week.
"Next July we'll get a full report back," he said.
"I'm very confident that what they'll say is what we want to hear, that is carry on Liverpool, carry on regenerating, carry on building on the back of World Heritage site status and we'll see you in the future."
Unesco has asked the UK to submit a report of its efforts to protect the Tower of London by February 2007.