Zac Goldsmith, Conservative MP and environmental campaigner who has threatened to quit over a third runway at Heathrow, told BBC Radio 4's Today programme:
"We haven't just lost Justine Greening from this department, we have also seen Theresa Villiers moved out, both of whom were absolutely rock-solid on this issue in terms of defending what is still the Government's line officially.
"I think their movement out of the Department of Transport shows the Government is at least trying to open the door to the possibility of a third runway."
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Drivers belonging to the RMT union are due to walkout at 9.30pm on Saturday in a dispute over a sacked colleague.
A new opinion poll gives the party an increased lead at the expense of the Greens.
The Rail Minister said it was not a matter of crowd control but passengers "trying to get home after a long day at work".