Other highly polluted areas include Oxford Street near Marble Arch, which registered at 150 micrograms, and Cockspur Street near Trafalgar Square on 138 micrograms.
The fourth and fifth locations were Park Lane and Knightsbridge - which measured 135 and 134 micrograms respectively.
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The plaque at number 16 Cowley Street in Westminster marks the brown brick Georgian townhouse where Sir John lived for 31 years.
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Metropolitan Police officer, Tom Harrison, has been crawling the course since the race began on Sunday morning.