It is not just that he has next to zero support among mainstream Labour MPs in the Commons; it doesn’t matter that he has rebelled against the party leadership ever since he has been in the House. Indeed, it doesn’t matter that he sometimes identifies the right problems – low pay, underinvestment in infrastructure, or whatever. It is his solutions that are so out of whack with reality.

This is a man whose policies are way, way to the Left even of the last Labour leader – Miliband – a man who in the end was resoundingly rejected by the electorate for being too Left-wing. Jeremy Corbyn is a bearded version of Ken Livingstone (I think they even go to the same tailor for their vests). He would take this country back to the 1970s, or perhaps even the 1790s. He believes in higher taxes and a bigger deficit, and kowtowing to the unions, and abandoning all attempts to introduce competition or academic rigour in schools – let alone reforming welfare.

Jeremy Corbyn takes 53% of support in new poll

He is a Sinn Fein-loving, monarchy-baiting, Israel-bashing believer in unilateral nuclear disarmament. It is nonsense to compare him to Michael Foot, who had been at least a Cabinet minister and before that a distinguished campaigner against the pre-war appeasers. This is a man who, for more than 30 years, has made a political career out of being explicitly and avowedly on the Spartist Left. He is a frondist, an inhabitant of the semi-Trot margin, an unrepentant lover of oppositionalism. Never in all his wildest dreams did he imagine that he might be leader of what has been – until this year – one of the major parties of government; and now he is having greatness thrust upon him.

How have the People’s party engineered this extraordinary horlicks? There are four groups of culprits. There is the Miliband regime, as mentioned, which not only came up with the deranged rules of the contest – by which, at one stage, the power to help choose the next Labour leader was handed to my old friend, the Conservative penseur Toby Young. Mili and co also shifted Labour so much to the Left that they managed to give a kind of spurious legitimacy to the Corbyn agenda. Miliband adopted wholesale the Livingstone playbook of state-enforced price freezes and rent controls and other attempts to buck the market.

There is a sense in which Corbyn is explicitly the heir of Miliband – and it is notable that Ed has kept a low profile lately, as if he realises the enormity of what he has done. The next group of culprits are all the New Labour old guard: Alastair Campbell, Mandelson, and above all Mr Tony himself – they have been cloth-eared in their response, hectoring Labour supporters who still haven’t forgiven them for the Iraq war; and as for Blair’s suggestion that Corbyn-backers “get a heart transplant”, it conjured an unfortunate image of our zillionaire former PM, jetting off to California for expensive organ-swapping procedures that are simply beyond the means of most people in this country.

The third set of villains is, of course, the other candidates, who have been so robotically dull that they have made Jeremy’s woolly ruminations seem positively electrifying. They are so torpid that it almost feels as if they want to lose. Come on, guys: where is the fire? Where are your plans to build a new Jerusalem? I cannot think of a single thing any of them has said – except to bash Corbyn, with the result that Corbyn is the story, Corbyn is the guy that everyone wants to see – and the loony Corbynmania grows, like a stock market bubble that will burst too late.

Which brings me to the group that bears final responsibility for what may – may, as I say – be about to happen: the armies of Labour rank and file who honestly seem to think that this might be the way forward. Yes, there really are a few hundred thousand people who seriously think that we should turn back the clock, take huge swathes of industry back into public ownership and massively expand the state.

The problem for Labour is that they do not represent the majority of people in this country. That is the real lesson of this campaign so far: that the mass of the Labour Party is totally out of touch with reality and common sense. How should we Tories react? Well, that is for another column; but in the meantime we watch with befuddlement and bewilderment that is turning all the time into a sense of exhilarating vindication: I told you they were loony.