A team visiting the Unesco World Heritage sites the Tower of London, the Palace of Westminster and the Abbey is concerned about their "visual setting".
A World Heritage Committee official said there were no "buffer zones" between the sites and 20 ongoing or new developments to protect the views.
If the team decides the sites are threatened, it could place them on the UN's Heritage in Danger list.
The government said it could not afford to see the iconic monuments downgraded.
A spokesman for the Department for Culture, Media and Sport (DCMS) said if the sites - which include St Margaret's Church in the Westminster group - appeared to be heading for the Heritage in Danger List when the committee met in June 2012, it would bring "bad publicity" ahead of the Olympics.
There are 28 World Heritage Sites in the UK.
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