A week before a British election that was meant to be a foregone conclusion, Theresa May finds herself where no Conservative prime minister ever wants to be – neck-deep in political hot water in the genteel city of Bath.

Home to a comfortable Tory majority in the 2015 general election, this ought to be a parliamentary constituency where the passage of yet more polling should barely cause a murmur . May’s surprise decision to call another election was intended to raid deep into opposition Labour territory and bolster her narrow majority of MPs in time for forthcoming Brexit negotiations.

Instead, the vicar’s daughter who inherited the keys to Number 10 Downing Street after the Brexit referendum result forced the early departure of David Cameron has watched her 20-point lead in the national opinion polls evaporate. Now she is forced to defend stronghold seats like Bath rather than dream of a landslide victory on Thursday.

Just why the former home secretary has lost her reputation for being a safe pair of hands is vividly apparent during a visit to an engineering factory just beyond the city’s Georgian stone splendour. Despite rehearsing her well-drilled message that only a “strong and stable” Tory majority can force a palatable outcome from EU negotiators, May is berated by a woman from the company’s export office who wants to know how it is going to sell its products without access to the European single market. Another factory worker demands to know what on earth she was doing proposing a so-called “dementia tax” in the party’s disastrously-received election manifesto.

Though Brexit remains popular nationally and equally problematic for her Labour opponent, Jeremy Corbyn, he has succeeded in shifting the debate to social issues. An hour earlier, he decides to upstage the prime minister by agreeing to a televised debate that night. A previously supine British press pack is suddenly shouting about why she is not willing to attend the debate. Outside the factory, a crowd has gathered to reprise a hit chant from the end of the last period of Conservative dominance in the 1990s when local MP Chris Patten also lost this seat: “Tories out,” they shout. May’s “strong and stable” mantra looks more and more like a millstone.

An election poster at the West Yorkshire Cricket and Bowling Club. Photograph: Pool/Getty Images

Despite its dominance of 20th century British politics, the Conservative party has a curious knack for shooting itself in the foot. Sir Edward Heath, a predecessor of May’s who was the last to ask the Queen to dissolve parliament ahead of time and call a “snap” election, found that his rallying cry “who governs Britain?” was met with the wounding answer: “Not you.” That 1974 election was the first to take place after Britain joined the European Economic Community. “Do you want a strong government which has clear authority for the future to take decisions which will be needed?,” asked Heath in an eerie echo of Theresa May. Against the topsy-turvy political backdrop following the 2016 referendum to leave, the United Kingdom is perhaps in even less mood to be taken for granted now.

Despite its dominance of 20th century politics, the Conservative party has a knack for shooting itself in the foot

Whether Corbyn really threatens an upset as shocking as the Brexit result or the election of Donald Trump remains to be seen. Despite a dramatic narrowing of some national polls, the same opinion sampling industry which showed him beyond all hope a couple of weeks ago remains almost as loathed and suspect as the political establishment. Traditional polling companies, which weight responses according to historic turnout rates, show May with a still comfortable two-digit lead.

Upset can only really come if Corbyn defies demographic inertia and persuades millions of young people to come out and vote for his message of income redistribution and free university tuition. “Experts brand [polls] utter tripe,” blasted the Europhobic Sun newspaper when May first appeared to stumble. For Labour, the closest political analogy is neither Brexit nor Trump, but Corbyn’s American political doppelgänger Bernie Sanders, who was coincidentally in Britain this weekend for a book-signing tour to explain why he lost.

An upset victory for Jeremy Corbyn can come if he defies demographic inertia and persuades young people to vote. Photograph: Andy Buchanan/AFP/Getty Images

Nonetheless, Britain’s parliamentary system offers some intriguing possibilities even if this year’s fiery leftwinger fails to ignite political revolution. Despite her current majority of 17 MPs, May called the election to give herself breathing room ahead of tricky Brexit talks that start on 19 June. With Labour in apparent disarray after disastrous local government elections, Tory strategists had hoped she might even win the sort of three-digit lead not seen since Margaret Thatcher or Tony Blair. Now the prime minister is warning voters that the loss of “just six seats” is all that stands between her and a potentially unstable alliance led by Corbyn.

Coalition governments have had a suspiciously foreign feel in Britain since the Liberal Democrats (Lib Dems) helped prop up Cameron’s first government, and Labour currently insist they would not enter into a formal alliance with either the Lib Dems or Scottish Nationalists (SNP). But since both these two smaller parties are passionately committed to remaining in the EU, a so-called “hung” parliament could test the resolve of either of the two dominant supporters of Brexit.

Britain’s ongoing political uncertainty also comes against a backdrop of fading economic growth and rising security fears. The national shock following the terror attack in Manchester, and irritation at the way details of the police investigation were leaked by US security sources, has only underlined how dependent Britain is on international alliances that have been thrown into turmoil by Brexit and Trump.

May’s latest political dilemma is how to respond to Trump’s rejection of the Paris climate accord: join the G7 outrage and risk offending her last international ally, or continue to provide only muted criticism and risk being accused of inheriting Blair’s role as poodle to a loathed American master?

The election that was meant to be all about Brexit has turned out to be anything but. National security, social affairs, even a surprise Tory proposal to bring back fox hunting, all are looming almost as large in the minds of voters as they head back to the polls on 8 June. May had predicted this would be hunting season. She did not expect to find herself in the role of the fox.