Daniel Hannan is an MEP for South-East England, and a journalist, author and broadcaster.

This might startle some ConservativeHome readers, but here goes. Britain has been lucky in the temper of its main left-wing party. You don’t have to look very far to find radical parties that were born in bloodshed and revolt; that wanted to strangle the last king with the entrails of the last priest.

Labour, though, stood aside from Europe’s sanguinary socialist tradition. Its roots were not in revolution, but in brass bands and the temperance movement, in nonconformist churches and working men’s libraries. Its aim was not to pull people down, but to raise people up – to disperse power, to spread opportunity as widely as possible. Morgan Philips, the former colliery worker who served as the party’s General Secretary through the middle years of the twentieth century, liked to observe that Labour owed more to Methodism than to Marxism, and he was spot on.

Which leads me to a second observation that some readers might find startling. The degeneration of the Labour Party ought to alarm all of us, even the most tribal Tories.

It’s not just that, without an opposition, we are in danger of becoming flabby and self-serving – though that prospect is dire enough. It’s that the dissolution of what was, until recently, a great national movement will leave no equivalent force in its place.

I’ll say this for Jeremy Corbyn: his commitment to avoiding personal attacks in politics is wholly genuine. The decent old boob never imputes base motives to opponents – something that is more unusual in public life than it ought to be.

The same is not true of many of those who have joined the Labour Party in his name, for whom politics is mainly about invective. “Let’s all get together and have a good hate,” is how George Orwell mocked the far Left of his own generation. He’d have had Momentum’s number. To give a telling, because trivial, example, when a sweet-natured little girl on Channel 4’s Child Genius on Tuesday night chose Margaret Thatcher as her special subject, the Corbynistas on Twitter exploded, calling her unprintable names, hoping that her parents would be involved in a traffic accident, and worse. If that is how they respond to a nine-year-old child, we should hardly be surprised by the tone they take with the people they regard as Blairite traitors.

Then again, the Blairites must shoulder their share of the blame. There has always been a sour and sociopathic fringe Left in this country but, until now, it has been precisely that – a fringe. What brought it into the mainstream was the failure of the established Left. During the Blair/Brown years, the Labour Party turned its back on its own electorate. It became a corporatist party, a party that seemed more at ease in Davos than in Darlington, a party that lined up with tax-exempt Eurocrats as they preached austerity and the euro from their private jets.

What is left of Philip Morgan’s party? Or, if you prefer, of Ernie Bevin’s party, or Barbara Castle’s party, or Gwyneth Dunwoody’s party or even John Reid’s party? (Gwyneth Dunwoody was Philips’s daughter – his lineal as well as his ideological heir.) Sure you can still find a couple of dozen Labour MPs in that tradition: John Mann, say. But many more Labour parliamentarians are as sundered from their base as Tony Blair was.

Labour MPs, Labour activists and traditional Labour voters now occupy three separate circles, that barely interlock. It can’t last. The party is heading for a formal split.

Although historians will tell you that the SDP was formed because of differences over unilateralism, the economy or the EEC, anyone with first-hand experience of elected politics will tell you the true reason: incumbent Labour MPs were being threatened with mandatory reselection.

How history repeats itself. Now, as then, the threat of unemployment will make many Labour MPs jump before they are pushed. Now, as then, they will dress up their decision with high-flown language about creating “a radical centre” or some such. Now, as then, they will in all likelihood merge with the handful of surviving Liberal MPs.

And then what? It has to be reckoned likely that, at the next election, some kind of SDP Mark II will field candidates against official Labour candidates around the country. Our electoral system ruthlessly punishes such splits, and the Conservatives could expect to win a parliamentary majority wholly out of proportion to their share of the vote. (UKIP, which might have been the beneficiary in several northern seats, seems intent on disembowelling itself even faster than Labour.)

If you’re rubbing your hands at the prospect of easy Tory victories, I’d ask you again to ponder the fate that eventually overtakes all unchallenged parties. We’d face two unelectable alternatives: one angry and extreme, the other remote and metropolitan. With no one to keep us on our toes, we’d become factional, complacent and, in time, sleazy.

And what of that chunk of the electorate who believe in what Labour used to stand for? Without a respectable party to represent them, will they give up on politics, or switch to a less respectable party?

I’d urge the people’s party to pull itself together, but I’m afraid we’re past that stage. Soon this won’t just be Labour’s tragedy; it will be Britain’s.