Police are understood to be searching for chemical substances at a London property after two people were arrested under anti-terror laws. A 19-year-old man and 36-year-old woman were arrested in Streatham and Stratford.
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The high of 35C was recorded on a Bakerloo line train between Piccadilly Circus and Oxford Circus at 2pm.
Weather forecasters say temperatures could reach 35C, beating the previous record of 34.6C in the scorching summer of 1976.
After years of political manoeuvring over the future expansion of Heathrow Airport, there has been an important development this lunchtime.