A couple of weeks ago on BBC Radio 4’s Any Questions I was singing the praises of Britain’s most likely future Opposition leader.

The brilliant thing if Jeremy Corbyn wins the Labour party leadership race, I argued, is that by testing to destruction in Britain the same ideology that has already been tested to destruction in Castro’s Cuba, Stalin’s Soviet Union, Mao’s China, Kim Jong Il’s North Korea, Enver Hoxha’s Albania, and so on, he will make the Labour party unelectable for at least a decade.

I joked that in honour of the earnest beardie I was even thinking of wearing a Jeremy Corbyn vest, just like the ones he favours – bought, apparently, for just £1.50 from his local market.

But now – like quite a few others, ranging from former Labour Prime Minister Gordon Brown to former Tory MP Louise Mensch and columnist Janet Daley – I’m beginning to realise that frivolity may not necessarily be the most sensible response to a man who was cosying up to the IRA weeks after the Brighton bomb that nearly killed Margaret Thatcher and who describes Hamas as his “friend.”

My worry is not so much that, as received wisdom has it, that all governments need a credible Opposition leader to hold them to account. (By that token, Margaret Thatcher’s run as prime minister – with Michael Foot and Neil Kinnock leading the Opposition benches – would have been a complete disaster, which I’m not sure it was). Rather it’s that as Janet Daley argues here, it’s that Corbyn represents the kind of hard-left revolutionaries who’ve given up on parliamentary democracy altogether.

What the hard Left is now aiming for is a different sort of power altogether: the kind that is achieved by revolutionary activism through industrial disruption. By seizing the means of production and distribution directly through strikes and organised demands, the Left can take control of the levers of national life without any of the tedious hassle of legislation and parliamentary argy‑bargy.

This is the doctrine of direct action that has always been accepted by activists as a legitimate alternative to governmental power. It is what used to be known, when these things were debated openly at every Marxist salon, as anarcho-syndicalism.

Or to put it another way, Jeremy Corbyn doesn’t want to find an accommodation with the capitalist system as Tony Blair sought to do and even Gordon Brown imagined he was doing. Like his predecessor Red Ed Miliband, only more so, Corbyn is an unreconstructed Marxist for whom free markets are the enemy.

I think this goes a long way towards explaining his, ahem, Jewish problem.

It’s entirely possible, I suppose, that some of Jeremy Corbyn’s best friends are Jewish. But if he is a massive philosemite, he does have a funny way of showing it with some of the company he keeps and the events he attends.

Besides being close to Hamas and Hezbollah, he has described Muslim hate preacher Raed Salah as an “honoured citizen” (and invited him for tea at the House of Commons) and advocated an anti-Israel boycott in the aggressively pro-Palestinian Electronic Intifada.

Then there is perhaps the most damning evidence of all: the fact that Yasmin Alibhai-Brown has come to his impassioned defence.

Anti-semitism is bang on trend in left-wing circles these days. A friend who attended a dinner party in the company of various Labour grandees – including a former senior minister from the Blair era – reports that the hatred towards Jews in general and Israel in particular was so blatant it was like attending an editorial meeting of Der Stürmer.

But I don’t think it’s a fashion thing that has led Corbyn in this direction. (This, remember, is a man so unconcerned with outward appearances that he wears vests and dines on little but tinned baked beans). Nor do I think there’s anything personal to this animus. (By most accounts he is a perfectly genial fellow who wouldn’t hurt a fly, let alone dream of entering a ghetto with a Schmeisser and yelling: “Kinder! Raus! Schnell!”)

Rather, my guess is it that’s a purely ideological thing. Corbyn’s problem with the Jews, au fond, I suspect is the same one the French Left has with them now and the Germans had with them increasingly in the years after the First World War and that a certain kind of upper class Englishman had with them in the Twenties and Thirties.

Basically, if you don’t believe in free market capitalism, then the Jews are an affront to human decency.

God knows how you’d feel if you were an unreconstructed Marxist and you looked at the disgraceful performance of the Israeli economy – averaging a growth rate of nearly 4.3 per cent a year – while those of all its Arab neighbours were tanking. My guess is that you’d think it was jolly unfair and that you’d want to bring them down a peg or two. Nothing personal, but as someone almost said, you can’t make an omelette without secretly yearning for there to be a smoking radioactive hole where Tel Aviv used to be.