For the Labour left’s many enemies, there are few events more useful than a leftwing defeat. Not just for its immediate consequences, which have been graphic over the past week as Jeremy Corbyn’s messy but transformative four-year leadership has been reduced by his critics to a single bad election campaign. But also for the longer term ways in which such a defeat can be deployed: to attack leftwing politicians in general, close off leftwing policy options, and ultimately deny the Labour left’s right to exist. The left rarely gets to run the party and so is all the more castigated when it fails to capitalise on the opportunity.

On election night, the former New Labour minister Alan Johnson began this familiar ritual – describing the pro-Corbyn group Momentum, which has 40,000 members, as “this little cult”. “I want them out of the party,” he said on ITV. “Go back to your student politics.”

It was a powerful intervention, widely noted by the rest of the media. Johnson, like quite a few other leading New Labour figures, had once been on the radical left himself. Before becoming an MP “I did consider myself to be a Marxist”, he confessed to the New Statesman in 2004. Yet in the view of New Labour’s still vocal grandees, their descendants in today’s party, and most political journalists, such attachments are just youthful indiscretions. Grownup Labour politics is centrist. And whenever the party breaks that rule, disaster follows.

Until last week the main evidence for this conviction was the general election of 1983, cited again by Tony Blair on Wednesday in a speech attacking Corbyn’s leadership. In that campaign Labour, led by Michael Foot, offered voters a leftwing manifesto, and was crushed by the Conservatives – who went on to govern for 14 more years. Labour eventually returned to power, it has long been argued, only because it abandoned its radical policies and marginalised those in the party who had come up with them. After last week’s disaster, say Corbyn’s critics, Labour should do the same.

Yet there are big differences as well as similarities between the party’s defeats in 1983 and 2019. These differences tell us important things about the state of the party now, and about its prospects. But unless the Labour left persuades others that this election was not simply 1983 revisited, it risks again being ostracised for decades, to the detriment of the party as a whole.

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For a start, 1983 was much worse in many ways than 2019. Back then, the Conservatives won a majority of 144, compared with 80 last week. In 1983 Labour got 27.6% of the vote – its worst share for 65 years. Last week it got 32.2% – mediocre, but more than at the 2010 general election, when Alan Johnson was home secretary, or in 2015 under Ed Miliband. This year Corbyn may well have been “a disaster on the doorstep”, as Johnson put it; but such assessments conveniently omit to mention that New Labour, in its latter years, was an even harder sell.

And unlike Foot, Corbyn won the support of a cohort of voters that will only become more important. According to the Conservative pollster Michael Ashcroft, last week Labour received almost three times as many votes from the under-35s as the Tories. In 1983, the Tories led Labour comfortably in this group. Then, Margaret Thatcher’s party often seemed more modern than Labour, offering a vision of an individualistic, competitive country, which many young people liked. There was an intellectual ferment on the right, which for years had been producing fresh policy ideas.

Few people would say these things about the Tories now. In 2019, their almost content-free manifesto, and massive reliance on older voters, were highly effective as election tactics. Yet, like the airy promises to increase state spending in today’s Queen’s speech, they are also signs of a party with questionable long-term prospects. By contrast, Labour’s youthful support, and policies addressing what are by common consent the biggest contemporary issues – the climate emergency, the inadequacies of the modern economy and Britain’s proliferating social crises – suggest a party with the potential to do much better at future elections.

And even some of the similarities between 1983 and 2019 are less terrifying for the left than many think. In both contests, Labour struggled against an unexpected surge of nationalism that swept up many of its traditional voters: the triumphalist aftermath of the 1982 Falklands war; and the 2016 vote for Brexit. Such episodes aren’t that common, despite the best efforts of the tabloids, and their electoral effects don’t usually last. In 1983 the Tories drew level with Labour among working-class voters, but by the next election Labour was well ahead once more. With Brexit likely to fade as an issue, and given the failures of past Tory governments to do much for the working class, it’s not hard to see a similar process happening again.

Play Video 'I want Momentum gone': Alan Johnson slams Labour left – video

In a democracy as prone to changing its mind as Britain, political settlements and orthodoxies never last for ever. Even the view that Labour’s 1983 manifesto was completely misjudged looks less convincing now. Foot’s proposals for tighter controls on banking and a less militaristic foreign policy may have been “suicide”, as the left-bashing Labour MP Gerald Kaufman famously described it, when put before the jingoistic, increasingly materialistic electorate of the early 1980s. Yet, given the way the Iraq war and financial crisis destroyed New Labour’s credibility in government, perhaps his manifesto wasn’t so naive after all.

In the 80s, one of Labour’s biggest electoral problems was that it often performed poorly in London. In 1983 it won only 26 London seats, less than half the Tories’ total. Yet Corbyn’s election to parliament that year as a scrawny young radical was an early sign that Labour would come to dominate the capital. Despite the fact that London has become ever more central to British life since, Labour’s strength in the city – its total of 49 MPs there was unchanged by last week’s election – is now presented by the party’s critics as a weakness.

Labour’s regeneration after 1983 made little use of its London MPs, and instead revolved around clever young centrists with northern constituencies – such as Blair, who won Sedgefield for the first time in 1983. This approach eventually worked, with much help during the 90s from John Major’s hapless Tory government; but it didn’t create a lasting ascendancy. New Labour’s vote dropped successively in 2001, 2005 and 2010. And last Thursday Sedgefield, like many of New Labour’s former northern strongholds, elected a Tory MP.

After last week Labour could look for a different path to recovery, acknowledging that the left of the party, for all its failures this time, understands the modern world and the emerging electorate in ways that centrists, at least so far, do not. Yet if the party is too busy blaming the left for everything, this route to power will not be found.

• Andy Beckett is a Guardian columnist and author of Promised You a Miracle: Why 1980-82 Made Modern Britain