Last week, I asked whether it was ever appropriate for a government to take military action without prior parliamentary approval.

At the time when I wrote that article, we did not know exactly what action the government, in concert with the French and US governments would take in response to the chemical weapons attack in Syria. We now know, of course, that the action was rapid, self-contained, highly targeted and aimed at degrading chemical weapons facilities whilst minimising any collateral damage and avoiding loss of civilian lives.

And there was a considerable majority in parliament in favour of the action once it had occurred.

There was, however, a very interesting debate about whether the government should have sought prior approval.

It turned out that a majority of MPs saw no need for prior approval in this case. But what was very interesting was the degree to which, in the course of the debate, distinctions began to be made between different kinds of action under different circumstances.

Everybody in the House of Commons agreed that, in the event of a direct attack on the UK, it would be right for the government to act immediately in whatever way would best protect us.

At the other end of the spectrum, it seemed to me almost universally agreed that, where a government was proposing a long-term series of military actions which would or might involve putting large numbers of lives at risk and which might be difficult to unwind in any short period, there was a clear need under the existing conventions for parliament to be consulted in advance and to give its approval. However, between these two extremes there was an interesting and as yet unresolved debate about the threshold at which prior parliamentary approval would be required. In this grey area, there were many different views about what the current convention really means - and hence about what the constitutional position currently is or ought to be. We are seeing our constitution evolving before our eyes.