Talk about scoring an own goal.

David Cameron's call to Conservative MPs not to go through the division lobbies with Labour MPs, whom he described as a "bunch of terrorist sympathisers", was a terrible mistake even if Foreign Secretary Philip Hammond sprang to the Prime Minister's defence this morning.

As the debate got under way, Mr Cameron hit the right tone in the Commons having clearly got carried away at his meeting with Tory 1922 committee backbenchers.

Yet, in this battle for hearts and minds, his key audience is not his Conservative chums - we expect only around a dozen not to support the UK Government motion - but Labour MPs, some of whom are still undecided faced with such a major, complicated issue.

Jeremy Corbyn and his loyal lieutenants have been trying to persuade swithering colleagues to vote against extending airstrikes. They claim, and I think rightly, that some of them are drifting towards the No camp.

The Labour leader condemned Mr Cameron's outburst as a "desperate slur" which demeaned his office, which, in the circumstances, few could disagree with. Senior Tories were out desperately trying to limit the damage.

The Foreign Secretary insisted the PM's remarks were not aimed at long-standing opponents of war like Mr Corbyn, whose views he said were "obviously sincerely held".

But Mr Cameron's outburst has added some extra political spice to a marathon debate that will be heated and passionate.