Daniel Hannan is an MEP for South-East England, and a journalist, author and broadcaster. His most recent book is What Next: How to Get the Best from Brexit.

A month after the outbreak of the Second World War, John Maynard Keynes wrote a famous letter to the New Statesman:

‘The intelligentsia of the Left were the loudest in demanding that the Nazi aggression should be resisted at all costs. When it comes to a showdown, scarce four weeks have passed before they remember that they are pacifists and write defeatist letters to your columns, leaving the defence of freedom and of civilisation to Colonel Blimp and the Old School Tie, for whom Three Cheers.’

Keynes wasn’t being entirely fair. There were plenty of patriotic Leftists in 1939, even among the intelligentsia. He was, though, describing a certain type of Leftist – the type for whom hatred of British military action trumped every other consideration, including basic human rights.

Can you think of anyone like that today? A vegetarian throwback to the 1930s? An abstemious, well-intentioned, republican, bike-riding, bearded, anti-colonial crank? Someone who would rather side with Putin or Assad than accept that the UK’s intelligence services might have a point about something?

It is important to understand Jeremy Corbyn’s Weltanschauung, his way of looking at the world. It would be unfair to call the Labour leader pro-Putin. The Russian autocrat runs precisely the sort of nationalist, crony-capitalist, militaristic state that, in other circumstances, Jezza would loathe. But when it’s Putin versus May, he can’t bring himself to back a Tory government – any more than he could bring himself to back Margaret Thatcher against Galtieri’s fascist dictatorship.

A conviction that Britain is always on the wrong side guides Corbo’s response to the latest barbarities in Syria. I’m not suggesting that he has a duty to back military action. The issue of intervention was always a finely balanced one and, to be honest, I’m not sure that the latest alleged chemical attack tips the scales either way. Assad has carried out far worse atrocities with conventional weapons. You can argue that we have a moral duty to intervene, or that a proportionate use of force now would serve our strategic interests; alternatively, you can argue that intruding will do more harm than good, or that it is none of our business. One more apparent use of poison gas doesn’t alter the fundamentals.

The trouble is that Jeremy Corbyn is not simply making a case for non-intervention. He is, as over the Skripal affair, taking the Kremlin line, namely that this is all a very fishy business, that you can’t trust claims made by the West and that Russia should be involved in the final settlement. Just as Sinn Féin spokesmen, asked to condemn Republican murders, would trot out platitudes about wanting “all the killing in Ireland” to end, so Corbyn speaks in deliberate cliché: “I condemn all violence from wherever it’s come from”.

It’s reasonable to be cautious. In war, claims and counterclaims are brandished freely, and facts are hard to come by. The balance of evidence suggests, for example, that the Assad regime was responsible for the 2017 sarin attack in Khan Sheikhoun but, almost exactly a year on, we still don’t know for sure.

Dictators have learned how to exploit the West’s slow verification processes. They know how mercurial public opinion is in democracies. They understand that, as the Player King puts it in Hamlet, “what to ourselves in passion we propose, the passion ending, doth the purpose lose.”

Britain’s authorities eventually showed, with impressive precision, who had murdered Alexander Litvinenko, but events had by then moved on. We may in due course find definitive proof of Assad’s complicity in breaching the chemical weapons convention but, again, the moment for direct retribution will have passed.

Putin is a master of delay and dezinformatsiya. He has pursued the same strategy over Salisbury and Douma. From the moment the chemical attacks were reported, bizarre counter-theories were concocted, some of them laughable – such as the suggestion, made by the Russian Embassy, that Britain had abducted the Skripals. The purpose of these preposterous claims is not to convince, but to confuse. You’re not meant to come away thinking that Britain has kidnapped Yulia Skripal (having first nearly murdered her and then, for some reason, nursed her back to health). You’re simply meant to shake your head cynically at all claims, to disbelieve the BBC and Fox and CNN as much as you disbelieve RT.

The former KGB officer in the Kremlin doubtless can’t believe his luck at finding that Britain’s Opposition is led by a man who will gladly go along with such nonsense, a man whose first instinct in a national crisis is to treat it as a way to attack the Tories.

Ask one question. In what conflict has Jeremy Corbyn ever been on Britain’s side? He has shown himself willing to back any cause, however vile, provided it is sufficiently Anglophobic: the IRA, the USSR, Hezbollah. He couldn’t even bring himself to condemn ISIS without tacking on a criticism of the American presence in Iraq. To repeat, it’s not that Jezza wants to emulate these movements. He disapproves of their human rights violations just as, during the Cold War, he used to urge Communist states to become more democratic. But, in the last analysis, he will always find a way of blaming the world’s problems on Britain, America and Israel.

When the Warsaw Pact was still in business, people who took such a line were called useful idiots. They would do the Kremlin’s work without needing to be bribed, it was said, because their idealistic Leftism blinded them to the true nature of the Soviet tyranny.

Now, though, Corbo doesn’t have even that justification. In making excuses for Assad and Putin, he isn’t backing some notionally Leftist cause. He is lining up, rather, with France’s National Front, Austria’s Freedom Party, Hungary’s Jobbik, Spain’s Falange, Greece’s Golden Dawn and his own newest British supporter Nick Griffin. A useful idiot? That’s putting it kindly.