Like the Conservatives, its century-or-so-old opposite number, Labour was until very recently a proper political party – that’s to say, one whose MPs, members and supporters were united in campaigning for it as a prospective party of government.

Labour’s gradual erosion under Tony Blair and Brown (from its record majority to date in 1997 to below 30 per cent in 2010) was followed by its near wipe-out in Scotland at a Parliamentary level in 2015.  This made bouncing back in 2020 to win a working majority a very tall order indeed.

Jeremy Corbyn’s re-election as Labour’s leader with an increased percentage of the vote (from 60 per cent to 62 per cent) confirms that it has given up on winning outright in 2020 – and indeed as a mainstream political party as the term is usually understood.

Momentum is often compared to the Militant Tendency, and in policy terms such an exercise is valid.  But it misses an important point.  The Militant generation were pre-Facebook, pre-Twitter, pre-internet, pre the new technology.  Its life’s mission was to gain power.

It is not at all clear whether this is also true of their modern successors.  Sure, most of the new members who have flooded into Labour presumably believe that Corbyn can indeed win the next election.  And, certainly, they have joined in droves.

The Party how has over 650,000 members – more than three times more than the Conservative total of around 200,000.  Furthermore, Corbyn took 59 per cent of their support this second time round, a nine per cent rise in his backing from the first time, when the new category of registered supporters drove his victory.

But there is little evidence to date that Momentum and their allies are willing to put in the hard work that previous generations did.  They have been willing to sign up to Labour en masse; they are plainly more than happy to rampage all over social media, shouting down anyone who disagrees with them (or trying to).

Some have delighted at the opportunity over the summer to turn up and cheer their hero as he plodded towards his inevitable victory over Owen Smith.  But talking to oneself is not the same as talking to others.  And swarming all over Twitter is not the same as putting leaflets through doors, or knocking on them.

Labour MPs, who by the nature of what they do come into contact with many non-party members – and have to take of what they think – know this.  They grasp that if Corbyn is still in place in 2020, Labour will be cruising for a bruising.  That’s why three-quarters of them have expressed no confidence in him formally.

They thus face a choice.  They can try to make their peace with Corbyn, and hope for a front-bench job.  Or they can form themselves into a new grouping, inside Parliament and maybe outside it.  Or they can sit tight and hope that something turns up.  The third is the most risk-free option, and many will presumably take it.

What is happening to Labour is not unique.  Conventional parties of the Left are in trouble in Spain, Greece, France – almost everywhere you look.  In very simple terms, the gap over immigration between the politicians who run them and the voters who elect them has become a gulf.

Labour in Britain is thus really two parties.  The first is the Labour of parts of London: Camden, Greenwich, Islington, Lambeth, Haringey: pro-immigration, prosperous, pro-globalisation, largely middle class.  Then there is the rest of the party, based largely in the Leave-voting, anti-migration midlands and north.

Squaring that circle would tax a more ingenious politician than Corbyn.  As it is, Labour’s members are not, by and large, even trying: Smith’s intellectual surrender to the Left was proof of that.  Instead, they are soaring up, up and away into a fantasy world.  The date of the party’s return from it is uncertain.