Grosvenor Place, which runs alongside the Queen's London residence, had the highest level of the toxic gas nitrogen dioxide in 2012.
Researchers found 152 milligrams of the gas per cubic metre of air, with a main contributor being diesel engine fumes. The EU legal limit is 40.
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Research into property prices has found London has more areas with an average price of more than £1m than anywhere else in the UK.
A permanent memorial will be unveiled today in memory of murdered Middleton soldier Lee Rigby.
The desk and chair where Charles Dickens sat to write his final novels have been bought for the nation using a national heritage grant.