Workington Man was having a peaceful smoke outside the Henry Bessemer pub when the word “politics” triggered a furious torrent.

“Politics? You mean Brexit and all that? I’m sick of it, absolutely sick to death. Let them do what they want, I don’t give a shit any more, excuse my language. I’m sick of listening to them, no one gives you a straight yes or no. I know I should vote, but sod that. I can’t be bothered any more,” said Anthony McMillin, 60.

McMillin comes from a “whole family” of Labour voters, and he voted Labour in every election until two years ago, when he switched to Ukip. He left school at 16 for a job in the local steelworks, which lasted three years until the plant closed in 1975. Then he was a swimming pool attendant, and later played in a band until the gigs dried up. Now he just about gets by, treating himself to the occasional pint at the Henry Bessemer, a Wetherspoons establishment named after a 19th-century engineer and inventor.

McMillin’s biography largely fits the profile of “Workington Man”, the invention of a right-leaning thinktank Onward to describe the cohort of voters it says the Conservative party must win over if Boris Johnson is to secure a majority at next month’s election. Onward’s report said Workington Man was over 45, white, without a degree, voted Leave in the 2016 referendum, worried about crime, and “favours security over freedom”. Workington, on the Cumbrian coast, is “one of the places where the eponymous archetype is most common among the local electorate” and is “the ultimate bellwether seat, despite being a longstanding Labour stronghold”.

According to Will Tanner, the thinktank’s director: “It is clear that the Conservatives’ path to victory runs through working-class rugby league towns like Workington, Warrington and Wigan … as well as the party’s leafy heartlands in the south of England.”

A newspaper billboard in Workington this week: ‘Workington Man’ is the invention of a right-leaning thinktank. Photograph: Christopher Furlong/Getty Images

Workington Town, the local rugby league club, swiftly issued a statement setting out its “apolitical” credentials. Implicitly disassociating itself from Workington Man, the club said: “We cater for a broad church of fans, players and volunteers of all backgrounds, ages and gender, and always have done.”

Like Worcester Woman, Mondeo Man and other erstwhile target voters, Workington Man may disappear as quickly as he rose to prominence. Nevertheless, the Conservatives wasted no time in announcing a multibillion-pound funding package for towns in marginals in England’s north and the Midlands, aimed at revitalising high streets and supporting small businesses. Meanwhile, Nigel Farage said he would visit Workington this week as part of the Brexit party’s bid to win over disaffected pro-Leave voters from both the Conservatives and Labour.

The sitting Labour MP, Sue Hayman, who is defending a majority of 3,925, dismissed the Workington Man epithet. “It’s extremely old fashioned to try to put people into narrow, cliched categories,” she told the Observer. “To assume all people who have a certain type of job and enjoy a certain type of sport and have a certain type of education are all going to vote in the same way is deeply patronising. I also couldn’t believe, in this day and age, that women have been completely ignored.”

Apart from a three-year aberration, Workington has elected a Labour MP for the past 100 years. But its once muscular industrial base of shipbuilding, coal and steel has long gone, and in recent years traditional identities have fractured. Now, the main employers are the nearby Sellafield nuclear plant and a Swedish-owned paper factory, which has hinted at job cuts in the coming months. Tourism, farming and small food production form the basis of the local economy.

‘Some constituents tell me they want to leave with no deal, some ask me to negotiate a good deal, some are desperate for me to promote Remain and a public vote’: Workington’s Labour MP, Sue Hayman. Photograph: Anthony Harvey/Rex/Shutterstock

It is Britain’s least diverse constituency, said Hayman, and has a population ageing at twice the average national rate. “Due to lack of industry and job prospects, young people leave, and older people come to retire because it’s beautiful.”

Unlike almost 60% of her constituents, Hayman voted Remain in 2016. “I’ve had a number of people come to my surgeries to say, ‘Why have you voted against Brexit?’ I always say I’d be irresponsible if I did not hear what businesses are telling me about the economic impact on my constituency.”

She listened to everyone, she said. “Some constituents tell me they want to leave with no deal, some ask me to negotiate a good deal, some are desperate for me to promote Remain and a public vote, some don’t care. Not everybody cares about Brexit.”

She was sceptical about whether the Tories would invest significantly in targeting her constituency, pointing out that the Conservative party was defending even smaller majorities than hers in two other Cumbria seats, Carlisle and Copeland. She will base her campaign on defending the NHS and expanding local transport infrastructure – “the things that people really care about day to day, what affects their lives” – but acknowledged that Brexit would be a significant factor.

“I don’t think there’s any point in worrying. I’ve been the MP for four and a half years, a lot of people know me, and I think people will vote on different issues. I will just have to wait and see what people want to vote on. And if ultimately that means I lose my seat, then that’s what happens.”

Of the dozen or so Workington Men approached by the Observer last week, none said they intended to vote Labour

The Conservatives’ hopes of taking Workington will have been boosted this weekend by a Survation poll for the Daily Mail which found that they were on course to win by more than 4,000 votes, with a 10-point swing from Labour. It may be ill-advised to give credence to any poll. But of the dozen or so Workington Men approached by the Observer last week, none said they intended to vote Labour. More than half insisted they would not vote; a few said they were undecided; one planned to vote for an independent candidate, and one said he would vote for either the Conservatives or the Brexit party, “whichever gives the clearest promise to come out”.

Tony Wareing, 71, a local businessman and chair of the Workington Heritage Group, said he recognised Workington Man among friends, associates and neighbours. “He is typical of most of the industrial towns throughout northern England that have traditionally voted Labour. That’s changing because of Brexit. This is a Labour town but it’s on the brink of change. Most people voted to leave, and it hasn’t happened, and they are very fed up. It will be the issue that decides the election here. Labour voters might not switch to the Conservatives – they will probably just not vote.”

The local Brexit party candidate, Philip Walling, a former barrister who writes books on rural issues and has never belonged to a political party before, hoped to persuade disaffected Labour voters to back him. “I’ve heard a lot of people saying they are sick of the political classes and they won’t vote,” he said. “But there are also an enormous number of people saying, ‘I’ve always voted Labour, and I can’t stomach the Tories, but I’m prepared to vote for you.’ They are Labour Leavers, and there’s no other place for them to go.”

In the European elections in May, the Brexit party topped the poll in Allerdale borough, which incorporates Workington. On a 34% turnout, it got 38.5% of the votes cast, with Labour on 13% and the Conservatives on 9.5%. Farage’s visit to the town this week is likely to make a splash, and no doubt prominent Tory and Labour figures will be hot on his heels.

Hayman feared it could become “a quite unpleasant and aggressive election”. Despite an “enormous amount of abuse: ‘traitor’, ‘witch’, the death-threat thing”, she had never considered standing down. Instead, she was braced for a challenging campaign, the outcome of which was far from certain. “I think it’s going to be very volatile and it’s difficult to judge what’s going to happen at this stage.”