David Cameron has reached out to political opponents as he tried to defuse the row over a third runway at Heathrow Airport.
Mr Cameron said he would not renege on his vow to block a new runway during this Parliament but did not rule out such a measure after the next general election in May 2015.
Labour MP John McDonnell (Hayes and Harlington), who has campaigned against a new runway, asked him to block a new runway while he led the Conservative Party.
The Prime Minister said: "While I do believe we need to establish a form of review that will bring parties together and make a decision about airport capacity, I will not be breaking my manifesto pledge."
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London was today a city of sirens and half mast flags in the wake of another terror attack.
MPs said they would "carry on" and go to work "as usual" in defiance of the terrorist attack outside the Palace of Westminster.
A huge police operation is under way after a terror attack in Westminster.