"We understand that a foot of concrete burst into the control room having been poured into an escalator void.
We await further information but what we do know is that LU technicians are on site now working flat out to clear up the mess and get services back on line, proving once again that its directly employed public sector staff who are needed to deal with this kind of emergency, making a nonsense of Boris Johnson's tube staff cuts plans."
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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.