Like many thousands of other people, I joined the Labour party after its defeat in the general election. In fact – fickle me – I joined it for the third time, having originally signed up when Harold Wilson was leader, subsequently leaving under James Callaghan, joining again under Blair, and leaving again under Brown. A pattern of unsteady behaviour that was unconnected to the personalities of these politicians, attractive or otherwise, and sometimes not even to their policies. The Iraq war was the best reason to leave – this isn’t hindsight – and yet I carried on paying my dues for years afterwards.

My motives for membership have never been very clear to me. Sceptics don’t make good campaigners. I’m not an energetic helper or organiser. In any case, there are all kinds of ways to support a party without joining it. By voting for it, for example. Since 1970 I’ve voted Labour in every general election, whether I was a member or not, partly because my MP for the past 30-odd years, Jeremy Corbyn, has always been what’s called a good constituency MP, quick to answer a letter and take up a case; and also because I once saw him browsing in a second-hand bookshop, a habit that to me suggests refinement and decency. (Questionable, I admit: few politicians have been keener browsers of second-hand bookshops than the Rev Ian Paisley.) And yet this summer, weeks before Corbyn became a leadership candidate, I joined the party again. Why?

The reason was partly practical. Christian Wolmar, a friend, needed votes at a local party meeting to get him on the shortlist of the six people who want to be Labour’s candidate in next year’s contest for London mayor. As it happened, I couldn’t attend the vital meeting – I was useless to Wolmar’s cause and on the face of it, I’d wasted £45 or so on the annual membership fee. But, of course, I’d also joined for other reasons that are harder to explain. I suspect the same applies to the several thousand who joined the Lib Dems as well. Our behaviour came out of a surge of pity and concern for the defeated, combined with a fear of what their untrammelled victors might get up to: there was – I can’t be sure – some thought that we needed to “show solidarity”, if only with the past.

I had an inkling of this in the earliest days of the campaign. A friend in northern England, canvassing for the Greens in an old textile town, wrote to say that he believed the Labour party in its present form was finished and would need to be remade. It was run by “chumps”. Its near extinction in Scotland was widely predicted, but my friend said it would also take a battering in the north from Ukip. How would I vote? I said Labour. Why? Because, I said, I felt sorry for it. My friend found my reply ridiculous, and yet looking at Ed Miliband, that’s what I felt. Of all the post-mortems into the cause of his defeat – that he was too far to the right or to the left or not “business friendly” enough – it was Peter Wilby in the New Statesman who offered the simplest and best explanation: that Miliband was a clever man who, unfortunately, was no good at politics.

In contrast to the opinion polls, my friend in the north was prescient about the effects of this. What he didn’t expect, as an active Green and a former longtime member of the Communist party – latterly among the party’s prominent intellectuals – was an email from Harriet Harman inviting him to help decide Miliband’s successor. “Thank you for being part of all this, Peter [not his real name],” Harman wrote. “There’s no need to register to vote – you’re already eligible and will receive your ballot paper by email nearer the time.” My friend was intrigued. He discovered, he wrote to me, that “as a member of the Bankdam Warpers and Wefters Society [not its real name], which is affiliated to an organisation called the National Union of Labour and Socialist Clubs, which I have never heard of, I am de facto a signed-up supporter of the Labour party. By clicking on one link and agreeing that I do not actually ‘oppose’ Labour, I am now entitled to vote [for a leader]. Harman has taken a personal interest in my actions. And it has not cost me a penny, not even the much touted £3 [the fee for ‘supporters’].”

He thought he would vote for “Jez” Corbyn. He felt “sentimentally entitled” to vote for him. But the fact that Labour had extended the franchise to outsiders – some might say enemies – such as him suggested, he wrote, “that a once-great political party has really descended to the depths”. And certainly, in the light of his experience, the idea that the party has either the means to identify hostile entryists or the right to bar them from voting, having so unfastidiously encouraged their entry in the first place, now looks like fanciful nonsense.

Meanwhile, he and I and 600,000 other affiliates, supporters and members (the last like stupid people sitting in economy who have paid the full fare) endure an immense bombardment of emails and texts from a party that has taken social media to its heart. Not only from the four leadership candidates, but from the five people who want to be their deputy, and in London the six people who want to be chosen as the mayoral candidate; and not only from these 15 principals but also from numerous secondaries – fans and celebrity endorsers who want to persuade you of their candidates’ fine qualities and stainless careers.

There are some memorable sentences and moments. Alan Johnson, backing Tessa Jowell for mayor, assures us that no other politician inspires such warmth: “Tessa is a star. She is Labour’s Kylie – everyone loves her and she only needs a first name.” Nancy Dell’Olio, never known as just Nancy, invites us to share a fun evening of “drinks and mingling” with deputy leadership candidate Ben Bradshaw. Caroline Flint, another contender for deputy, has a video entitled “You may feel you know me”, in which she stands without makeup on a stage, and with those words begins an appalling summary of her impoverished early life, absent dad and alcoholic mum, to convince us that “I have never had a sense of entitlement”. She does convince us – move us even – though the truth is that Flint has spoken about this before, and to that extent, we are right to feel that we know her.

As for Corbyn, my friend at the Warpers and Wefters used to say of him, fondly enough, that he was more NGO than politician – the champion of the underdog wherever one could be found. This is true, and I was struck by David Miliband’s warning in the Guardian this week that a Labour party that was merely a pressure group would mean Britain would become what he called “one governing-party state”. His argument is persuasive, until you consider that Britain is now a problematic political entity and that Scotland under the SNP is much more a one-party state than England under the Tories.

Who is to blame? Jez, at least, had nothing to do with it. We would have to start with the dear old centrist Labour party that David, Liz, Yvette and Andy so want to preserve.