In the wake of recent events, looking back at the morning of 6 May 2005 feels like surveying an altogether more innocent era. With jihadists allegedly massing at the gates and Tony Blair affecting all the grave resolve of a war leader, the idea that the Prime Minister might have expressed even the merest flicker of humility and contrition may seem deeply unlikely, but it is there on the record. "It is clear that the British people wanted the return of the Labour Party, but with a reduced majority," he said. "We have to respond to that sensibly, wisely and responsibly."

Left-leaning hearts may have fluttered at the idea. Mine certainly did, though the pleasure did not last long. As Blair told reporters that he had "listened and learned", I took part in a hastily arranged post-election debate on Radio 5 Live, which also involved the Scots MP Eric Joyce, the loyal ex-army major who can be relied upon to promote the government line with credulous enthusiasm.

By writing a book and co-authoring a website advocating a modest level of protest voting, he said, I had done something "disgraceful". There was no way back to the fold for me: my only option was to abandon hope of a realigned Labour and join the Liberal Democrats.

And so the depressing realisation dawned: far from creating a spirit of conciliation, the fright delivered by the election result had actually served to make some of Labour's Manichaean absolutist tendencies even worse. Four months on, they seem to have reached a new peak, as evidenced by recent whispers that Blair's post-7 July performance had joined that allegedly "historic" third victory in the rationale behind calls for him to go for a fourth term. If the aforementioned MP played his role in some of this, then its topsy-turvy ludicrousness might merit the use of a literary adjective: these are indeed Joycean times.

Out in the fields, unfortunately, Blair's absurd personality cult collides with rather grimmer circumstances. How many Labour members would instantly recognise a description in the latest edition of Renewal, the Labour quarterly, of a constituency party in Birmingham that "does well to get 20 people to a meeting", whose members' average age is "around 60" and whose organisation is kept afloat by "around 12 people, including the MP and workers in his office"? Here lies a sobering counterweight to all that triumphalism - and, perhaps, a deserving focus for some of the Prime Minister's proposed sense, wisdom and responsibility.

In two of the election's most celebrated constituencies, however, that's not quite how things have worked out. Earlier in the summer, I visited Blaenau Gwent, where local suspicions that an all-women shortlist was being used to shoo in a Blair loyalist had led to a dramatic upset: the loss of Labour's safest Welsh seat to Peter Law, the local Welsh Assembly member who resigned from the party to romp home as an independent.

The story rather suggested a Valleys version of the Ken Livingstone experience, though its aftermath was very different. In London, circa 2000, Labour had been sensible enough to leave its Livingstone-supporting members well alone, whereas Blaenau Gwent has suffered a veritable purge: 20 Law supporters (some of whom have been Labour members for upwards of 50 years) summarily expelled from the party, one for the heinous offence of writing an off-message letter to the Western Mail. Labour's local crisis has since worsened: June brought the loss of a dead-cert Labour council seat to an independent, and there is seditious talk of a new "Real Labour" political grouping.

This past week, I received news from Hornsey and Wood Green, the inner-London seat where disaffected activists stayed at home and Labour's 11,000 majority was lost on a 15 per cent swing to the Lib Dems. Here, again, arrogance and rancour seem to have taken precedence over any kind of healing process. One erstwhile Labour councillor has been expelled for advocating a reduced parliamentary majority and drawing attention to two tactical-voting websites in the correspondence columns of the Ham & High; and three long-standing activists are under investigation for taking part in an item on the Today programme. According to one, the councillor's claim to have contributed nothing that breaks party rules might not count for much: a local official told her that he's more concerned with what she might have said "when the microphone was switched off".

Such is one of new Labour's more contorted ironies: that people who espouse support for this most futuristic of political projects indulge in an almost medieval kind of zealotry, while once-loyal party supporters adopt rather more modern habits - chiefly, taking their votes elsewhere.

John Harris is the author of So Now Who Do We Vote For?. This is the latest in a series of political columns by guest writers