PMQs: John McDonnell calls Cameron liar on Heathrow Airport
18 December 2013 Last updated at 13:19 GMT
A Labour MP appeared to mouth the prime minister was a liar following their question and answer about airport expansion.
John McDonnell told David Cameron that people had "lost all faith in him as a man that keeps his word" over a Conservative pledge not to build an extra runway at the west London airport in this Parliament.
But David Cameron said he had "stuck with that promise" and urged people to read the report by Sir Howard Davies on airport capacity "before they start shouting across the House of Commons in a completely inappropriate way".
The Speaker then stepped in to tell members: "I know what I am doing, I don't need any help from backbenchers."