Parliament de facto accepted last night something that we already knew. Tony Blair is a war criminal. As Anthony Barnett has pointed out, the consensus, across the house was that the then Prime Minister lied in order to take us into the Iraq war.

The correct thing to do with criminals is to put them on trial in front of a jury of their peers. If they are found guilty of something as serious as war crimes, that seems to me to be one of the rare occasions on which prison is a sensible punishment.

Even a passionate believer in penal reform such as I am has to accept that this seems to be a rare occasion on which, perhaps, the notion of deterrence might work.

This, more than ever, is what we must do with The Right Honourable Anthony Lynton Blair – banker, PR consultant, Middle East Peace Envoy and former Prime Minister of the United Kingdom of Great Britain and Northern Ireland.

The impact of failing to do so is now clearer than ever. If a leader of one country sees another get away with a breach of international law, then they are more likely to believe that they too will get away with such a violation.

If Blair can so obviously break international laws and then prance about the world stage, then why cannot Bashar al-Assad, in a messy civil war, authorise the use of chemical weapons (though of course it still isn’t at all clear that he did)?

Assad may fear a Western ‘rap on the knuckles’ intervention a bit. But unless it is likely to be targeted at him personally, will he really care that much?

Imagine this. Imagine if, in the middle of the night, tonight, Tony got a gentle knock on the door of his family home. A security detail would, presumably, open it. A team of police officers would present the bleary eyed officer with a warrant. In hushed tones, perhaps they would argue. And then, the guard would stand down and fetch his famous ward.

After a heated exchange in, perhaps, his pyjamas and the family kitchen, after some tears from Ms Booth, the former Prime Minister would be led away in handcuffs. Perhaps a journalist would have been tipped off – justice for the king of spin? I’d rather not – allow the man a dignified fall.

What then would Assad think? Would he fear that, for the rest of his life, he would be at risk of arrest? Would this deter him? Perhaps. And what would future leaders, considering breaching international law, learn? Would they be less likely to commit their crimes.

Of course, this won’t happen. The law is, most often, a tool of the powerful. Just as police officers are never punished for their crimes, neither are the global police. International crimes are committed by bandits, not prime ministers.

This may be a fantasy. But it is no more a fantasy than the idea that a few cruise missiles would will anything at all to help those suffering in Syria. And if we really wanted to send a chill down the spine of those who would breach the laws of the world, then this, surely, is what we would do.