Caroline Pidgeon, Leader of the Liberal Democrats on the London Assembly says spreading the closures over such a long period of time is more disruptive to passengers.
What do you think? Join us on Facebook and let us know how you'd prefer Transport for London plan closures like these. Does spreading the maintenance over 18 months work for you? Or would you prefer all the closures to happen at once?
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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.