Labour strategists believe repeat of 2015 election’s 30.4% support will be enough to keep leader in post – but without working-class voters even this looks unachievable

Will Corbyn remain Labour leader come what may? First, he must match Milliband's vote share

Jeremy Corbyn has declared his intention to remain as Labour leader whatever the outcome of the 8 June general election. “I was elected leader of this party and I’ll stay leader of this party,” he told BuzzFeed News on Monday.

His supporters have pointed to Neil Kinnock’s decision to remain at the helm following Labour’s 1987 election defeat, in which the party gained 20 seats and increased its share the vote by 3.2%.

Team Corbyn is reported to be ready to argue that he should keep the job – regardless of how many seats Labour loses – if he matches the 30.4% vote share garnered under Ed Miliband’s leadership in 2015.

What are the chances of this happening? Monday’s Guardian/ICM poll recorded a 22-point lead for the Tories, with Labour at 27% – three points short of Miliband’s 2015 performance. This number appeared to confirm the BBC’s projected national vote share in last week’s local elections.

But look deeper at the Guardian/ICM poll and one key detail stands out from the 2015 data: Labour has lost its lead among working-class voters.

Before the May 2015 general election, Labour held a marginal poll lead of 32% to 29% over the Conservatives among those pollsters class as C2 voters – the skilled working class – and by a thumping 45% to 25% among DE voters – semi-skilled, unskilled and unemployed.

But Monday’s poll suggests those numbers have flipped. Theresa May’s Conservatives are leading – for the first time in more than 20 years – with C2 voters by 43% to 31%, and with DE voters by a more modest 42% to 35%.

It is these numbers that give succour to Tory strategists who believe that the doors to Labour’s traditional heartlands are open for the first time since Tony Blair’s 1997 landslide.

Some argue that Corbyn’s 30% strategy has led to him forgoing a serious defence of Labour marginals to focus only on driving up the vote share in safe seats.

Facebook Twitter Pinterest Ed Miliband unveils the ‘Ed stone’ in the final days of the 2015 general election campaign. Labour garnered 9.3m votes. Photograph: Stefan Rousseau/PA

“I’m serious about winning the election,” Corbyn said on Monday “I’m serious about going out there. I’ve been in Worcester and Leamington. I’ve been in Warrington. I’ve been in Croydon. I’m going all over the country on this because ours is an election to win.”

Worcester is 58th on Labour’s target list of potential gains; Leamington is 68th; Warrington is 100th on the Tories’ list. Only Croydon Central, 3rd on Labour’s list, is a genuine marginal.

James Morris, a former pollster for Ed Miliband, suggests Corbyn’s campaigning points to a different strategy. “His visits to seats like Leamington and Worcester look stupid, but [they’re] not. He’s a turnoff for voters, so [it’s] important to keep him busy away from places [Labour] wants to hold,” he said on Twitter.

Having lost most of its traditional base – working class voters – Corbyn’s team may well be relying on thethree groups of voters in which the party still enjoys a lead: young voters, aged 18-24, with whom they are more popular than the Tories by 56% to 25%; students (51% to 31%); and black and minority ethnic voters (61% to 28%).

The trouble for Corbyn is that these are the three groups of voters least likely to bother casting their ballot on 8 June – only 41%, 45%, and 42% respectively say they are certain to vote, compared with a national average of 62%. There are also simply not enough of them to replace the working classvoters who have defected to Theresa May’s Conservatives since the Brexit vote.

The polls had been expected to narrow during the campaign as the minor parties, particularly Ukip and the Liberal Democrats, secured a more visible media profile. But the collapse of the Ukip vote in the local elections, and the evident struggle the Lib Dems are having in attracting Tory remain voters, means this is now unlikely.

Team Corbyn may believe it can match Miliband’s performance in 2015, when 9.3 million people voted Labour. But having lost its working-class core support, it is unlikely that even a strong showing among young people, students and Bame voters will help the Labour leader meet this already low benchmark.