The concourse at Waterloo was packed with frustrated commuters this evening, as services were affected by the hot weather.
South West Trains put speed restrictions in place between Clapham Junction and Waterloo - because the tracks were struggling to cope with surface temperatures approaching 50 degrees Celsius.
Trains were limited to 20 miles an hour, with many services delayed, cancelled or altered.
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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.