Just as Boris Johnson’s route to a Commons majority ran through places such as Grimsby, the battle for Labour’s future will also take place in its former strongholds. The postmortem of Labour’s biggest election defeat since 1935 is vigorous and ongoing, but in the provincial towns that make up its now-crumbling “red wall”, the debate seems to be done and dusted.

In interviews carried out since the start of the leadership race two weeks ago, 30 out of 33 Labour council leaders the Guardian spoke to said the party would be “finished” in their areas if Rebecca Long-Bailey became leader on 4 April.

They blame Jeremy Corbyn and the party’s confused stance on Brexit for the catastrophic loss of 59 seats, in many of which Labour voters ditched decades-long allegiances to vote for the Conservatives. A victory for Long-Bailey would simply continue the failed Corbyn project, many said.

“I do not want a continuity Corbyn candidate,” said Julie Dore, the leader of Sheffield city council. “It was the most disastrous result ever and we can’t just change the face, change the name, change the gender maybe, and just continue and do what we’ve done before.”

From Lincolnshire to Leigh and from Bassetlaw to Blyth, all but three of the Labour council leaders said either Sir Keir Starmer or Lisa Nandy were the party’s best hope of winning back voters. Most of all, they said, they wanted a leader who could connect with working-class voters while also holding Johnson to account at prime minister’s questions.

Although Nandy is considered an outsider – her polling among members lags way behind Starmer’s and Long-Bailey’s – she enjoys significant support among influential Labour figures in the north of England.

Facebook Twitter Pinterest Boris Johnson visits Grimsby fish market during the election campaign. Photograph: WPA Pool/Getty Images

“It has to be someone who isn’t in denial that we didn’t do very well at the last election, accepting that there is a different dynamic in leave seats,” said Linda Thomas, the leader of the opposition on Bolton council. Thomas knows all too well about the backlash from voters: her party lost control of Bolton council after 40 years last March.

Thomas said Labour had “perhaps not understood people’s pain enough” and that she believed Nandy would reconnect the party with voters in struggling areas. “There’s a feeling of disillusionment, being left behind. People are down on their knees and to be then told they don’t know what they’re talking about – people feel very patronised,” she added.

Quick guide Who do senior Labour figures in 'red wall' seats want as leader? Show Hide • The “red wall” was a huge block of Labour-voting constituencies stretching from north Wales into Merseyside, through Greater Manchester along the Midlands and up to the north-east. The origin of the term is unclear but some believe it was first used in 2019. • Thirty-three Labour leaders spoke to the Guardian and all but three supported Sir Keir Starmer or Lisa Nandy to become the party’s next leader. All of the 33 local authority areas voted for Brexit in 2016. • Of those who would disclose their least favourite candidate, all but two said Rebecca Long-Bailey. The other votes were for Jess Phillips and Emily Thornberry. • Labour leaders in six of the 10 longest-held Labour seats that fell to the Tories said they were backing Starmer or Nandy. They are the Labour leaders in Rotherham, Newcastle-under-Lyme, Leigh, Bassetlaw, North East Lincolnshire and Bolsover. The other four leaders had not responded to requests for comment.

Voters in leave seats felt they had been betrayed by Labour’s Brexit stance. The list of the 66 seats gained by the Conservatives reads like a roll call of left-behind towns, from the Midlands to the Scottish border, where the division over Brexit simply pushed leave voters further away from a party they had felt distant from for some time. In pro-Brexit, working-class towns such as Darlington, Redcar, Bolsover and Rhyl, the pattern was the same.

In the Nottinghamshire constituency of Bassetlaw, voters elected a Conservative MP for the first time in 90 years. Its council leader, Simon Greaves, said he was minded to vote for Nandy as he felt Starmer was responsible for steering the party towards the pro-remain stance that put off voters in his area. “I’m underwhelmed by the other candidates because I’m not hearing enough about what needs to be done to win back areas such as Bassetlaw,” he said.

Facebook Twitter Pinterest Keir Starmer gives his leadership pitch in Bury. Photograph: Gus Sivyer

Greaves said he was “incredibly disappointed” that the leadership hustings were taking place in the big cities instead of places such as Bassetlaw – one of a number of Labour leaders who expressed the same concern. “Even in terms of the campaign, the party seems to be turning its back on the east Midlands and people will take notice of that. If the party does not come here, the party is not listening to people from here,” he said.

In a Grimsby fish and chip shop this week, Nandy said it had been “humbling” to meet Grimbarians who had “consistently voted Labour but did not this time round”. The Wigan MP may be an outsider in the race but she is now guaranteed a place on the final ballot, in large part thanks to the backing of the GMB union on Tuesday. The uphill task will be convincing enough Labour members that she is the right person for the job.

Facebook Twitter Pinterest Lisa Nandy in her Wigan constituency. Photograph: Lorne Campbell/Guzelian

On the outskirts of Grimsby, the town’s Labour leader, Matthew Patrick, said Nandy or Jess Phillips would get his vote – before the latter withdrew from the race on Tuesday. “I wouldn’t necessarily rule out anyone,” he said. “But when [Long-Bailey] says that Jeremy Corbyn’s leadership scores a 10 out of 10 – it’s difficult to look at the result last year and see for the Labour party 10 out of 10 or anything even close to that … To be in this position after 10 years in opposition means there’s a lot of soul-searching to do.”