We are in the Royal Oak pub in Cannock, near Birmingham, on a miserable Wednesday night. Labour MP Gloria De Piero is buying a large round of drinks. “We had a bloody awful election result and we want to know why,” she tells a focus group of eight middle-aged men and women. All have been Labour voters at some time in their lives, but several have recently deserted to the Tories.

As she hands round beer, wine and soft drinks, De Piero, the MP for Ashfield, looks each of them in the eye. “We want to know how we win people like you, all of you, back to Labour.”

Ever since Jeremy Corbyn won the Labour leadership in dramatic circumstances last September, Labour has been consumed by debate about whether the revolution that delivered him represents a dead end for the party, or a new dawn.

The shift to the left has electrified the Labour base, but many party MPs fear it will alienate the wider public, including critical groups of floating voters on the middle ground, potentially keeping the party out of power for a generation.

For months at Westminster there has been dark talk of leadership plots. But among the expanded core of new members and supporters who propelled Corbyn to office, there is a belief that an evangelical push throughout the country can convert the necessary numbers. In the dozens of marginals Labour needs to win, does that feel like a plausible hypothesis?

The Observer accompanied De Piero and her shadow cabinet colleague Jonathan Ashworth, MP for Leicester South, as they headed across the country in search of answers in the key seats where Labour failed so catastrophically last May. A year on, council elections will give an indication of how Labour is doing. So what is the mood?

Cannock Chase constituency was typical of the disasters that hit Labour one after another on election night, proof that, despite five years of Tory-led austerity, its support was draining away in the former industrial areas which were its stronghold. It was number 50 on Labour’s target list of marginals and a must-win. The Tory MP who took the seat in 2010, Aidan Burley, had stepped down after organising a Nazi-themed stag party and, pre-election, the omens were good. Labour poured in resources. But to no avail. The Tories ended up increasing their majority.

It was the same story in several other key Midlands marginals. For the Labour party locally it was, as one official who worked seven-day weeks for two years put it, “demoralising and depressing beyond our wildest nightmares”.

The two shadow cabinet ministers want to confront the deserters face to face. De Piero and Ashworth ask for honesty from the assembled focus group, selected by the polling organisation Survation – and get it.

Mike Elliott, a former oil industry worker and trading standards officer in the West Midlands, says he will not vote Labour again, until it regains some economic credibility. “I am afraid I can remember the 1970s and the 1980s. I don’t think the Conservatives are running the economy well, but I think they are running it better than Labour would,” he says. There is broad agreement that the Tories – while not the party they would ideally want to vote for – are the least worst option as stewards of the nation’s finances.

De Piero looks on anxiously as it becomes clear that Paul West, one of the eight, will be the lone voice who is happy with Labour and Jeremy Corbyn. “I like what he says and I think people will get used to him,” he says.

The discussion remains about leadership for long periods. Sandra Dudley says she liked Ed Miliband but admits that he “just didn’t have it”. Dudley mentions Corbyn: “I know appearance is superficial, but people judge people by their appearances and when you see politicians in their smart suits, and then Jeremy Corbyn is there, he looks like he has just come off his allotment, and people aren’t drawn to him.”

Cindy Faulkner, a children’s books illustrator, chips in: “And he didn’t even sing the national anthem, which I think is most disrespectful because it means he doesn’t give a tinker’s toss about the Queen or he doesn’t know the national anthem – and if he doesn’t know the national anthem, that is disgraceful.”

The group gives its views on how to improve public services, particularly health and education, and all parties come in for criticism. But leadership returns time and again to the fore. Robert Jones, a former local authority worker and his wife, Judith, who worked in banks, arrive late and join in to take pot shots at Corbyn.

“When he sits there at prime minister’s questions, you think, ‘who let you in there?’ – he looks totally out of place,” says Robert. Judith then mentions Trident, which will become a recurring theme on subsequent visits. “Without some sort of defence, how are we going to stop, as an island, any sort of invasion that comes our way?” she asks.

Sandra Dudley adds: “We need a deterrent and we desperately hope we are never going to have to press that button but, if we haven’t got the deterrent, we are wide open.”

We move on days later to Kingswood, on the eastern outskirts of Bristol. Formerly a mining village, it was number 41 on Labour’s target list last May but Tory MP Chris Skidmore increased his share of the vote from 40% to 48.3% as Labour’s fell from 35% to 29.6%. This time, De Piero and Ashworth just want to meet people on the street, in cafes, out shopping, rather than repeat the focus group inquisition. Unsurprisingly, many look blank when asked about the state of Labour.

Ashworth talks at length to a man running a market stall who tells him he is not interested in politics or in voting and never will be, and they move on.

Evrim Tekim, the young manager of the Table Care Lounge Bar, says that when he has time to focus he still favours Labour and his friends on Facebook tell him that, under Corbyn, “it is all good and has a good feel about it”. In his cafe there are a couple of women drinking coffee who say they quite like Corbyn and one, Joy Penhaligon, says she could be tempted to vote for him because he is mild-mannered and comes over as honest. “He seems a nice, gentle man. He seems quite genuine to me.” But on a neighbouring table Sandra Weaver, a solid Labour voter and a close follower of politics, is unimpressed. “I think the party loyalists will vote for him whatever, but whether he will be prime minister is another matter. I am not convinced. I believe in Trident, put it that way.”

Yvonne Kelly, who runs Kingswood Florists, and who has never voted anything but Labour, tells De Piero she has not tuned in much to the political scene recently but the one thing she does recall about Labour is that Corbyn did not sing the national anthem. “He might have his opinions and all that but I wasn’t happy about it.”

This may be just a snapshot and a random sample in one shopping area in the west country, but there are more than faint echoes of views expressed in the Royal Oak in Cannock and if the Labour brand was ever strong here, it doesn’t feel like it is any more.

Enthusiasm for the new politics of Labour under Corbyn is strong among young Labour voters, so next we go in search of student enthusiasts and head for Southampton. Before hitting the university, De Piero and Ashworth canvass views in a council housing area of the Southampton Itchen constituency, where Ukip has been taking votes from Labour at local elections. This was the 22nd most winnable seat for Labour at the last election, but the Tories increased their majority from 192 to 2,316 votes on polling day.

Dan Jeffery, the local Labour councillor, says he has become worried that former Labour people are turning first to Ukip, then to the Tories. “You see it here. Someone who has voted Labour all his life then goes to Ukip. When he has broken the addiction of voting Labour, he feels he can vote Tory.”

On the housing estates, Ukip may have made headway but there is no obvious sign of strong loyalty to any party. Rather a sense that politics and politicians make no difference to lives. One man answers the door and says he voted Tory last time but can’t remember why. Another, who works in a supermarket, says Corbyn looks more like someone who should work alongside him at a checkout than someone he could vote for as a prospective prime minister. At the Spike Islander pub, Andrew White, who works in a warehouse, says he is solid Labour and will remain so. He likes Corbyn but doesn’t think he will be prime minister.

At Southampton University, De Piero and Ashworth have a canteen lunch with four leading lights in the student Labour club. “This is it. That is all we are, four of us,” says Ben Seifert, who was inspired to join the party by Corbyn and believes he should succeed. “The Labour party is the only credible force in British politics for equality and justice for all,” he says.

Clara Pope-Sutherland says she is annoyed by the way some Labour MPs are failing to rally round Corbyn and at talk of challenges to him so soon after he won with a huge mandate. “That upsets me. MPs need to rally round the person the party vote for,” she says. Only last week former paratrooper Dan Jarvis seemed to be laying out his stall in a speech, though he insisted he was only joining a healthy, open debate on Labour’s future.

Rob Bradshaw takes a different view to his fellow students and is sceptical about whether Corbyn can create a mass movement capable of winning the 2 million extra votes that Labour needs. “I think that everyone who will ever vote for Jeremy Corbyn has voted for him already,” he says.

Immigration has not been raised much across the tour so far but in Thurrock, in Essex – another former Labour stronghold where Ukip was involved in a tight three-way race last May – it is a dominant theme. De Piero and Ashworth say they found “real hostility” there from former Labour voters who had deserted to Ukip, interspersed with voter apathy and views that politicians never stand by their words.

Last weekend, in an interview with the Observer, Jess Phillips, the Labour MP for Birmingham Yardley, was asked whether she thought Labour could win in 2020 under Corbyn. “The honest answer is, ‘no, absolutely not’,” she said. The leadership is busy playing down its prospects for the May elections in England, Wales and Scotland. Corbyn and his inner circle are, however, taking a long-term view, pointing out that he and shadow chancellor John McDonnell continue to pack out halls up and down the country.

McDonnell wrote in this paper before Christmas that the challenge is to create a “mass movement capable of mobilising mass support to radically change our society”. That, he added, “requires a long-term, creative, patient socialism”. They have been underestimated before. They want time. Their challenge is to replicate the enthusiasm they mobilised during the leadership election and to spread it to the marginals where floating voters decide elections.

As De Piero and Ashworth can now tell them, they will have their work cut out.

• This article was amended on 13 March 2016 to change the headline for one that more accurately represented the text of the article.

