This is the official Turkish radar track of the Russian aircraft they shot down, in red. It briefly transited a tiny neck of Turkish land – less than two miles across where the Russian jet passed – twice. I calculate that each “incursion” over Turkish territory would have lasted about 10 seconds, assuming the plane was flying slowly at 600mph. That Turkey shot down the plane for this is madness, and absolutely indefensible. It is fairly obvious from the track that the plane was operating against Turkish sponsored Turkmen rebels inside Syria, and that is why the Turks shot it down.

But the inescapable conclusion is that the true madness would be for the UK to get involved in Syria and make a complex and volatile situation still worse, and risk being dragged into wider conflict.

To bomb ISIS in Syria is now legal in international law, with authority granted by the Security Council. (I subscribe to the argument of my ex-boss Brian Barder on the interpretation of SCR 2249). Whether it is wise or not is a quite different question.

Even John Simpson on the BBC yesterday admitted that many innocent civilians had been killed in recent bombings of the ISIS occupied city of Raqqa. Though being the BBC, while reporting correctly that the United States, France and Russia are all bombing Raqqa, they contrived only to mention civilian deaths in a sentence about Russian bombing. That bombing creates terrorist blowback has been proven beyond any rational dispute. So if ending terrorism is truly the aim, it is a curiously counter-productive means of going about it.

There is also the question of mission creep. In Libya, the security council mandated nothing but the enforcement of a no-fly zone, to prevent the possibility of a massacre in Benghazi, which was precisely as genuine a danger as Iraqi WMD. Quite illegally, the UK participated in a massive western air to ground attack including on populated areas, under the pretext of disabling any possible threat to western aircraft enforcing the no fly zone. The aim, quite illegal, was regime change. This is how “the no-fly zone was enforced” by western bombing of Sirte.

The danger is that a bombing campaign will cause this kind of devastation of civilian areas, as indeed is now happening in Raqqa, but also as in Libya will be carried far beyond the authorised objective, and extended against the areas loyal to President Assad. This risks confrontation with Russia – a danger that has been starkly illustrated since I started sketching out this article by the downing of a Russian jet by Turkey.

Libya illustrates starkly the last and largest problem – that you cannot control what fills the vacuum. The governance of Libya is now a disaster. The ultimate irony was that the people of Benghazi demonstrated their gratitude at being saved from “massacre” by slaughtering the American Ambassador. The truth of the matter is that, despite the dreadful records of both Saddam and Gaddafi, the manner of their removal resulted in a situation where life was undoubtedly better for the vast majority of the population under the dictators. Which is a massive testament to Western incompetence.

David Cameron appears to have no idea whatsoever what will replace ISIS in the areas under its control. We know that he does not want the Syrian state under President Assad to take control. The area is not Kurdish, so they are not an option. Hezbollah is regarded as an Iranian proxy. The West’s attempts to create moderate pro-Western Sunni rebel forces have been a pathetic failure. The Saudis and other Gulf states have funded a variety of rebels, including much of ISIS and other groups which have an equally insane agenda. If any of the Wahabbi groups besides ISIS could be strengthened sufficiently to hold major territory, they would undoubtedly be found to be just as enthusiastic at persecuting Christians and other minorities and beheading people.

Someone has to control the physical territory, and Cameron has no viable alternative for this at all. Talk of funding and training moderate groups is whistling in the dark. The USA has already put far greater resources into this than the UK ever could, and the result has been complete failure.

Having delivered Sikunder Burnes to the publisher, I have started research on a life of Lord George Murray, working title The Man Who Terrified London. It is in fact true that some Scottish aristocratic families deliberately allocated members to each side in the 45, to ensure continued family control of the estates. But such instances are very rare, the Frasers of Lovat being the most notable. Most family splits, like among the Murrays of Atholl, were genuine and painful. My favourite example is the MacDonells, who were all Jacobite but decided that Glengarry himself, a hopeless alcoholic incompetent, would do more harm to the Hanoverians by remaining on their side. There is an excellent simile here to the Saudis, where numerous minor royals and all their business contractors are pumping money into ISIS and other extreme Wahabbi groups, while the King and Crown Prince pretend to be pro-Western and anti-ISIS. That is when they can spare a moment from their aerial massacre of the Houtha, or sentencing children and poets to death at home. The situation in all our Gulf “allies” is the same.

It is of course instructive that there is no sense at all in which Trident missiles are helpful in this dilemma. It is worth repeating out loud every time we consider a defence or foreign policy dilemma “Trident is useless in the particular situation”. We should say it all the time. We are spending an inconceivable sum on a system which is no earthly use.

But bombing is just as useless. It can achieve nothing whatsoever except pointless death. It will make Cameron look macho and win some jingo votes, enabling the corporate and state media to whip up a frenzy of hate against non-militarists. I suppose that is a useful purpose for the establishment. There is no other useful purpose.

Bombing ISIS in Syria may now be legal. That does not make it useful or wise.