The Queen will be joined by members of the royal family for the annual Order of the Garter service today.
The sight of Garter Knights walking through the grounds of Windsor Castle wearing their lavish blue velvet robes and black velvet hats with white plumes is a colourful spectacle that attracts hundreds of people.
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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.