Saturday, too, marked the 25th anniversary of the attack on Halabja, in northern Iraq, when thousands died after bombs containing poisonous gases were dropped on the civilian population.

We can also see from Syria that there is a price for standing aside as well as intervening. We are close to the point already where a higher proportion of Syria’s population have died in the fighting than lost their lives in Iraq. I fear, too, when the civil war ends, that the growing influence that extremist factions have over the opposition will pose major problems.

There was nothing inevitable about the violence in Iraq after Saddam’s fall.

The overwhelming majority of Iraqis want a peaceful, democratic future.

It was a minority — supported by forces outside — who were determined to thwart these ambitions through violence.

Our security depends upon ensuring these extremists, wherever they operate, do not succeed. And this will inevitably, I’m afraid, lead to more difficult decisions in the future.