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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Police have released an e-fit of a man suspected of attacking her.
The force has been tweeting after carrying out a series of dawn raids.
Adenike Akingbogun made the dangerous manoeuvre after ignoring the crossing lights and driving onto the tracks.