Jeremy Corbyn’s Labour critics are already discussing how to respond if the party sustains heavy losses on election night – with most counselling against an early leadership challenge after his better-than-expected performance on the campaign trail.

Despite the narrowing in the Tories’ poll lead and Theresa May’s lacklustre campaign, most Labour insiders believe they are unlikely to advance on Ed Miliband’s 2015 tally of 232 seats.

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Many Labour candidates, particularly in northern seats away from the major cities, say Corbyn’s leadership is still problematic among some groups of voters, and the most pessimistic believe May could still secure a much-increased majority of 80 to 100.

Few in the party expect Corbyn to follow Neil Kinnock’s example in 1992 and resign straight after the result in the early hours of Friday.

In an interview with the Guardian, the shadow chancellor, John McDonnell, refused to acknowledge the possibility of defeat. Asked about whether he was worried MPs could be plotting on the backbenches, he said: “No, we are going to win this.”

He said that the Tories’ “foundations are crumbling”, with Labour receiving feedback on the doorstep about people struggling with living standards.

McDonnell said of the campaign: “It’s been terrific, the best I’ve ever been involved in, the atmosphere has been great and I’ve really enjoyed it.”

He said the first thing Corbyn would do as prime minister would be to tell voters that he understood the struggles they were facing.

“There will be a comprehensive programme to address the pressures that working people are under,” said McDonnell, promising to address pay and public services cuts, with a budget by mid-July.

If his optimism is misplaced, and Labour goes backwards, MPs who lose their seats are likely to voice some of their concerns at election counts in the early hours of Friday.

However, senior party figures have been advising that would-be critics should remain cautious, keen to avoid a repeat of the chaotic but failed “coup” against Corbyn’s leadership that began after the Brexit vote last summer.

Instead, they would like to see a calmer contest before the party’s conference in the autumn, with more than one candidate running against the Labour leader, in contrast to the ill-fated head-to-head challenge launched by Owen Smith last year.

Potential challengers being talked up include Keir Starmer, who has styled himself as “captain marginal”, touring the country to boost the morale of candidates in hard-to-hold seats,; Chuka Umunna, who initially stood in 2015 before withdrawing his name from the contest; and Yvette Cooper, who has attacked May over police cuts and maintained a high profile as chair of the home affairs select committee.

Corbyn’s allies, who may have a tighter grip on the parliamentary party if several centrist MPs lose their seats, could throw their weight behind Emily Thornberry.

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The final day of campaigning on Wednesday continued to emphasise counter-terrorism policy after last weekend’s attack in London, highlighting the absence of the shadow home secretary, Diane Abbott, from the political frontline.

After two missed media appearances on Tuesday, with Thornberry standing in at the last minute, Corbyn announced on Wednesday morning that the shadow policing minister Lyn Brown would stand in for Abbott for the remainder of the campaign.

It is understood that Abbott, who has suffered a number of tough media appearances during the campaign, has recently been diagnosed with a long-term health condition, which her doctors have been attempting to manage.

However, it is non-life-threatening, and not deemed serious enough to impair her ability to take on the job of home secretary if Labour wins the election. One of her senior shadow cabinet colleagues played down the seriousness of the condition, saying: “Everyone, in every job, gets ill from time to time. That’s just the way it is.”

Friends of Abbott denied reports that she had not been consulted before her break from the role was announced, pointing out that Brown is her deputy and the move could not have taken place without Abbott’s approval.

Speaking to reporters during her final round of campaign events, May wished Abbott a speedy recovery.

Corbyn told BBC Breakfast that Abbott had not been well for a couple of days and was taking a break from the campaign. He said: “Diane is somebody that works extremely hard and represents her community very well and I have to say has received totally unfair levels of attack and abuse, not just recently – over many years.”

In Watford on Tuesday night, at the fourth of six stops of the day, a slightly hoarse but energised Corbyn worked the crowd to cheers and shouts of his name. He cited the seat – currently held by the Conservatives with a 10,000 majority – as the one Labour needed to win to form a government, something he presented as still possible.

“Are you up for it?” he asked the crowd of several hundred people. “Are you up for the election of 2017? Are you up for rewriting history?”

Some of those in the crowd said before the speech they thought the idea of an outright Labour win was unlikely but most said they were hopeful of a hung parliament, or at worst a very small Conservative majority.