On a January morning 35 years ago, the Labour party split. The gang of four – Roy Jenkins, David Owen, Shirley Williams and Bill Rodgers – stepped out in east London’s Limehouse to declare their breakaway Social Democratic party. This anniversary would pass unnoticed, an arcane political footnote, but for the present state of Labour. Is Jeremy Corbyn a reprise of Michael Foot? Might history repeat itself? Pandemonium inside the parliamentary Labour party suggests anything is possible.

History first, for anyone under 50. In 1981 Margaret Thatcher was the most unpopular prime minister on record, recession and her extreme cuts causing soaring unemployment. Labour should have been demolishing her. But instead, plunging into the wilderness, it chose an unelectable leader pledged to unilateralism, and leaving Nato and the EU. The good policies in its 700-page manifesto – dubbed the “longest suicide note in history” – were drowned out. The SDP soared to an astounding 50% in the polls, but this firefly was soon snuffed out as victory in the Falklands revived Thatcher’s fortunes. Labour was out of power for 18 years.

In the Commons tea rooms, and wherever Labour people gather, that history is being replayed on a loop. With most Labour MPs convinced Corbyn can’t win and yet can’t be deposed, should the party split again? David Cameron and George Osborne are bent on an austerity far harsher even than Thatcher’s, heading for a size of state permanently below anything she dared, yet Labour lands no blows, makes no headway. Sliding by the month, it is trusted on the economy by only 18%, and is predicted to lose control of 16 councils in May, with a wipeout in Scotland, which Corbyn said he alone could save. Sadiq Khan’s expected win in London, a Labour heartland, offers small comfort.

Instead of aiming all their artillery at the Tory massacre of public services, Corbyn and his team divert attention, raising contentious issues not on most voters’ radar. The pro-EU case should be Labour’s to own, hammering wedges into the Tory split. Instead, from Corbyn’s camp comes a grudging near silence. Anti-Trident replacement might gain support, but Corbyn’s unilaterally declared unilateralism, refusing to pretend he’d press the button, rules him out of No 10 in too many voters’ eyes. Agreeing the phenomenal expense of new submarines but empty of nukes looks the worst of all worlds. Why raise talks with Argentina on “power-sharing” the Falklands, just after islanders voted 99.8% to stay British? Or with Islamic State, right now, really? What next, a united Ireland or handing Gibraltar back? All interesting discussions, but they are no route to winning the necessary 94 English marginals where Corbyn must woo some who voted Tory last time.

Time to split? Most Labour MPs are far removed from the party’s 220,000 new members, who dictate that Corbyn or someone of his views leads Labour. But here’s why an SDP-style split is unthinkable. New parties are always crushed by our first-past-the-post electoral system. There was never a better chance than in 1981 when four substantial national figures launched a left-of-centre party built on principles of social justice and internationalism in a yawning political vacuum, with Labour and Tories at their most extreme. But instead of “breaking the mould”, the mould broke them. You get one chance, and the SDP came within 2% of overtaking Labour in 1983, but crashed back to earth with 25% of the votes yielding just 23 seats.

Don’t do it, don’t think of it, Owen warns now. Good advice. For unlike Foot, Corbyn has compromised on Europe and Nato, so there is no single break point. And where is the idealism firing up Labour’s current social democratic wing, devoid as yet of post-New-Labour ideas or a fresh post-Corbyn radicalism? The SDP manifesto was well to the left of New Labour on everything, strong on redistribution – and constitutional reform and PR, still not espoused by Labour. Many who joined were drawn to its feminism: women’s quotas filled half the national committee and half of all shortlists, promoting women’s issues.

I was on the SDP national committee and candidate for Lewisham East, leaving me with memories of hope and despair, but also providing useful experience in writing about politics. I understand the bond MPs feel to constituency, having pounded every street, knocked on every door, every business and school. The sound of Chariots of Fire, our campaign tune, jolts me back to that illusion that surely you own this patch after so much hard work. Out with canvassers now, I see how few meaningful conversations are had for each doorstep day: “contacts” don’t mean votes – such monumental effort for so little return. Failure is abject, but political victory doesn’t bring much glory: odd how voters revere democracy, but revile its practitioners.

Rodgers, talking on Newsnight about the SDP last week, welled up as he recalled old Labour friends who cut him dead after the split. Schism breeds pure vitriol. Four Guardian writers stood as SDP candidates – and the rift within our office was venomous: some leftist colleagues picked up their plates and moved away from us in the canteen. In my Lambeth Labour party branch, Militant turned meetings poisonous, designed to eject non-believers. No wonder Labour people with long memories are wary of Momentum.

Breaking the mould with electoral reform would have transformed the political landscape, allowing a socialist and a social democratic party, a centre-right pro-EU Tory party and a hard-right faction for the likes of John Redwood and Liam Fox. Despite a meteoric launch, failure was in the stars for the SDP. Did we help pull Labour towards electability, or did the split stop Labour winning? That’s unknowable. The end was ignominious, as most of the SDP folded into the now moribund Lib Dems, while a rump SDP was humiliated at the Bootle byelection, overtaken by the Monster Raving Loony party. Heed the warning.

The reality is that Labour will win again only when enough ordinary members decide that ridding the country of this pernicious government matters most. No one wins unless led by the best future prime minister, most trusted on the economy. With two lost elections already, will deciding to win take another decade? Labour members would be better advised to learn from the last time and just cut to the chase.