Alison Munro, the chief executive of High Speed Two Ltd said: "This is a project that the country needs. The existing railway is becoming increasingly full and by the middle of the next decade parts of it will be effectively full.
"So we need to start now to plan to have that capacity in place."
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The station, which saw 44m people commuters use it in 2016/2017, will be transformed into a dining room complete with Christmas decorations.
Part of the monster fatberg will go on display in the Museum of London, while the rest of it will be converted into biodiesel.
Major engineering projects at key London stations mean hundreds of trains will be cancelled or diverted.