Boris Johnson has expressed frustration at the drawing out of the HS2 project timescale.
The Mayor of London wrote in The Telegraph that China built its own high-speed rail in just two years.
Meanwhile, he said, Labour are delaying the project further by "shamelessly courting the sceptic vote".
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The Office for National Statistics said gross domestic product grew by just 0.1%.
William's comments came during a surprise appearance at an event scheduled for just his brother.
Matt Campbell, who collapsed just a few miles from the finish line, had hoped to raise £2,500.