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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Their twisted romance revolved around fictional Facebook characters, and the 8-year-old girl was seen as a threat.
Passengers were forced to jump the ticket barriers to avoid being crushed by the crowd.
Soloman Bygraves followed 93-year-old Stanley Evans into his block of flats and pushed him over as he lunged for his wallet.