"Crossrail's success assumes the third runway of Heathrow because of the increased access it would give to Canary Wharf,” said Schabas.
However, Villiers insisted the Conservatives were fully to committed to Crossrail.
“It will go ahead,” said Villiers.
“As a consequence, Heathrow will be a much better airport, as it will be easier to get to and deal with surface pollution from cars.”
Villiers added that Tory money committed to building new high speed lines from London to Leeds, via Heathrow, Birmingham and Manchester would not reduce spending on existing lines.
"We have projected rail capital spend and we are confident it is affordable, and we remain committed to the existing rail network," she said.
New high speed lines would gobble 25% of the capital rail budget between 2015 and 2017, at a cost of £1.3bn per year.
Office of Rail Regulation chief executive Chris Bolt, who steps down in July 2009, said: "Contorl Period 4 [2009 - 2014] funding is the best the rail networks are going to get.
“Unless Crossrail does not happen for some reason, the budgets under CP5 will be very tight."