Post script 21:06
There are the five tests Ed Miliband has published this evening as conditions to be met for Labour's backing in the Commons. I reproduce them here for information:
1) We must let the UN weapons inspectors do their work and report to the UN Security Council;
2) There must be compelling and internationally-recognised evidence that the Syrian regime was responsible for the chemical weapons attacks;
3) The UN Security Council should debate and vote on the weapons inspectors' findings and other evidence. This is the highest forum of the world's most important multilateral body and we must take it seriously;
4) There should be a clear legal basis in international law for taking military action to protect the Syrian people;
5) Any military action must be time limited, it must have precise and achievable objectives and it must have regard for the consequences of the future impact on the region.