If the Brexit party wins the Peterborough byelection, it would return its first MP to Westminster just eight weeks after it was launched – a trajectory that took Nigel Farage’s previous party, Ukip, more than two decades.

And in a further sign of the fast-shifting fault lines of British politics, while Labour hopes it can retain the seat, the Conservatives, who held it for 12 years until 2017, are widely thought to be completely out of the running.

Thursday’s contest seems likely to hinge on two contrasting strengths: the Brexit party’s wave of popular support since last month’s European elections versus Labour’s established campaigning infrastructure.

The Brexit party candidate, local entrepreneur Mike Greene, concedes that the lack of election experience and voter knowledge is proving tricky.

“In an ideal world we’d have had that,” he says, taking a brief coffee break around the corner from a campaign headquarters crammed with cyan-rosetted volunteers. “The positive is that we’ve knocked on doors with an open mind, not knowing who were were going to speak to, and having a proper engagement with them.”

While bookmakers have Labour on odds as long as 6/1, a local source for the party insisted things were still “very, very close”.

“For us, it’s all about the get-out-the-vote operation,” they said. “Our vote seems to be there, but we need to get people out, and that can be tough in a byelection.”

Labour faces other challenges. The poll was triggered when Fiona Onasanya, who took the seat for the party in 2017, was ousted by a recall petition after her conviction for lying about a speeding ticket.

The new candidate, Lisa Forbes, is local and experienced – she came second in Peterborough in the 2015 general election – but has been criticised by Jewish groups for liking a tweet that said Theresa May had a “Zionist slave masters agenda”.

While the Conservatives have been somewhat ignored amid all this, Wayne Fitzgerald, who chairs the constituency party and is deputy leader of Peterborough council, insists they are still in the fight.

The Brexit party, he accepts, received a “tsunami of support” at the European elections: “The question is whether or not they can build on this – turn out people who would otherwise be watching TV, the people who only vote every now and then.”

But it is undeniably a difficult time for the Conservatives. At a heavily staffed Brexit party stall in the centre of Peterborough, John Stanyer, a former local Tory party chair who has left his Cumbria home for a week of volunteering, says he has bumped into several other ex-Tories.

“I’ve worked with them on a dozen campaigns for the Conservatives and they’re now all here, working for the Brexit party,” he says. “You can’t afford to lose that quality of people, the activists on the ground. When a party does that, at some point it reaches a critical point.”

Stanyer is utterly convinced Greene will triumph on Thursday: “It’s been like shooting fish in a barrel. I might end up looking like a complete idiot, but that’s how it feels.”

Also potentially being squeezed are the resurgent Liberal Democrats, and some Labour staffers predict that if Forbes does win it could be down to Lib Dem voters temporarily switching sides.

Chris Porsz, walking past the Labour stall in the city centre, voted Lib Dem in the European elections. As the son of Polish parents, a former paratrooper and a Holocaust survivor, who settled in Peterborough in 1947 he backs “a free, united, peaceful Europe”.

“But I might well vote Labour this time,” Porsz says. “A big part of that would be trying to stop the Brexit party.”

If Farage’s group does win it will mean not only a new political voice in Westminster but one represented by a self-professed novice.

Greene signed up to the Brexit party only four weeks ago after he was approached to stand by its chair, Richard Tice, and is still getting used to the media attention – he is smarting after the Observer described him as a “Keith Chegwin lookalike”.

While the party still has no policies beyond a no-deal Brexit, Greene is standing on a self-penned “four pledges for Peterborough”, promising to prioritise schools, further education, housing and jobs in the city, and to resist any party whipping which would go against these.

The specifics are, however, somewhat thin, and Greene concedes he has much to learn even on Brexit-related matters such as the Irish border.

“We’re a new party, seven weeks old. If I’m successful I’ll be a really new politician – I’ve only been in politics four weeks. But there’s a lot of people in the party with strong experience,” he says. “I will be defaulting to the experience and expertise of that team. I’m not an expert on many of those issues. And I’m happy to say that.”