-It's the largest event of its type in the UK and thousands of people are expected to visit central London to see West End performances for free all weekend.
-Performances are programmed on stage 11am-6pm on Sat and 12pm-6pm on Sun.
-Entry is on a first come, first served basis.
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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.