Boris puts pressure on DC.

Boris has told the nation he would lead the opposition if the Government u-turns on its policy for a third runway at Heathrow.

After Zac Goldsmith was threatening to resign again today, Boris later refused to rule out standing in a by-election so he can oppose the Government.

Though Cameron did say at PMQ's that he would not be breaking his manifesto pledge opposing a third runway at Heathrow.