Southwark Cathedral is the setting for Sadiq Khan's singing in as the new mayor of London, with politicians and even celebrities out in force.
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A number of people were treated at the scene at Oxford Circus by paramedics for coughing and lack of breath.
If temperatures stay high in the same spots for three consecutive days, the Met Office deems it a heatwave.
Some posts also linked to false press releases calling for the release of drill artist Digga D.