Now, I think it's a good idea that the lads in blue are keeping their eyes open at Heathrow for British citizens who've been fighting in the Middle East. I hope they are doing a thorough job of it – and I mean thorough.
I don't want to bump into a chap who's been firing missiles at Christian families in Syria. But on the other hand, I also don't want to bump into a chap who's been firing tank shells into the homes of Palestinians in Gaza.
In other words, I trust that the Met is keeping its watch for all potential criminals, whether their foreign military organisations carry the terrorist label or not. I don't know of any Palestinians who've been firing rockets at Israel and hold UK citizenship – Mr Plod should check them out too.
But it would be very interesting to know if the British Government is taking as close an interest as it should in any UK citizens – even if they have any other passports – who have been fighting in Israeli uniform in Gaza in the past couple of weeks.
Let me be frank. Dozens of British supporters of Israel do serve in the Israeli army. The same applies for Australia, New Zealand, Canada and the US.
And they don't necessarily gravitate to being war criminals. This may not be what an Arab would say – and it is certainly not what Israelis would suggest. But there is plenty of evidence – from 1982 in Lebanon, from 1996 in Qana, from 2008-9 in Gaza and again in Gaza these past two weeks – that individual Israeli soldiers and pilots have committed acts which, under international law, are war crimes.
I'm struck by the words of the co-director of the Israeli veterans' movement Breaking The Silence, Yehuda Shaul, who spoke at a meeting in Tel Aviv a couple of weeks ago about the brutalising effect of occupying other people's lands. Mass arrests, the liquidation of even a suspicious "silhouette", families paralysed with fear during searches.
"You adapt to it all," Shaul said. "The first time, you're in a state of shock, the second time, a bit less, and at the end of the week, you do it quite naturally." Interesting. It sounds as if Shaul is talking about being radicalised.
Isn't that what we say about certain other young British citizens with weapons who head off to the Middle East? But what are we to expect when Major-General Gadi Eizenkot – now a deputy chief of staff in the Israeli army – pointedly said in a newspaper interview six years ago that he would use disproportionate force on a village or city from which rockets were fired, famously adding that "from our standpoint these are not civilian villages; they are military bases"?
Which explains a lot of what happened over the past two weeks in Gaza. And as Muhammad Ali Khalidi, philosophy professor at York University in Toronto, points out, intentionally striking civilians in order to accomplish political ends is "the dictionary definition of terrorism". After all, isn't that what Hamas also does?
Let us hope and pray that no UK citizens have been involved in such terrible deeds. But it wouldn't be a bad idea, would it, if the lads in blue had a friendly word with them when they arrive back at Heathrow – and insist on knowing exactly what they were up to when they wore another country's uniform.