Labour and the Lib Dems have been warned they could hand the Tories victory in the crucial Mid Bedfordshire by-election by splitting the anti-Conservative vote.
A vicious war of words has erupted between the two opposition parties, who both insist they are best placed to seize the seat following the resignation of Nadine Dorries.
The former cabinet minister - who quit with a vicious blast at Rishi Sunak - retained the seat with a majority of 24,664 at the 2019 general election.
Despite that, the bookies have installed the Lib Dems as odds-on favourites to win the by-election, which is expected in October, followed by Labour and with the Tories a distant third.
But Tory peer and elections guru Lord Hayward said the Conservatives could still hang on to the seat.
He told the BBC: “Quite often in by-elections against a government there is an acknowledged main opponent, that’s been true for many decades now.
“What we’re seeing in Mid Bedfordshire is not only a very determined campaign both by the Labour Party and by the Liberal Democrats, but there’s also likely to be a strong independent as well, plus likely Greens and the like.
“If you have a split opposition, whatever circumstances it is, then what you may well get is the sitting party being able to retain the seat.”
HuffPost UK has spoken to senior figures in both the Labour and Lib Dem campaign teams, who made it clear that they would not be entering into any unofficial agreements to keep the Tories out.
Peter Kyle MP, who is co-ordinating the Labour campaign, said the party was “going all guns blazing” to pull off a historic victory.
He pointed to a recent Sunday Telegraph poll which put Labour in the lead, with the Lib Dems in fourth place.
“Since then our promises have firmed up,” he said. “We are going and re-engaging with residents and more people are coming across.”
Kyle, who is the shadow Northern Ireland secretary, said the Lib Dems “have not produced a shred of evidence to back up their claims that they can win here”.
He said: “The question for the Lib Dems is simple - where’s your evidence?
“Bookmakers BetFred are not Ipsos Mori or Opinium. People who put a flutter on politics aren’t the same as voters in the constituency. I’m baffled by the way they are acting - it’s strange and pig-headed.”
Despite recent Lib Dem by-election victories over the Tories - most notably in Tiverton and Honiton and Somerton and Frome - Kyle insisted Conservative voters are unlikely to switch to the party in Mid Bedfordshire.
He said: “This community has no history of voting Liberal in living memory. This isn’t one of those communities that goes Lib Dem or Tory.
“The idea that these particular Conservatives are suddenly going to go to the party that wants to re-prosecute the Brexit battles and that wants to legalise drugs is quite far-fetched.”
“I’m baffled by the way they are acting - it’s strange and pig-headed.”
A leaflet distributed to voters in the seat before Dorries eventually quit demonstrated the Lib Dem plan to attack Labour’s candidate, Alistair Strathern, for being a councillor in London.
A Lib Dem spokesman said: “It is very peculiar that they would pick a London councillor in a seat where the main beef people had with Nadine Dorries was that they didn’t like the fact she didn’t live in the constituency.
“You’re making it even harder for yourself if you don’t have a candidate who lives and works in the constituency.”
Labour insist that the Lib Dem criticisms are invalidated by the fact that Strathern was born and brought up in the constituency.
Unsurprisingly, the Lib Dems insist only they stand a chance of beating the Tories.
“We think that in a seat like this, Labour have a ceiling and it’s relatively low,” the spokesman said.
“There are lots of people who are unhappy with the government but are never going to vote Labour.”
On the possibility of an unofficial Labour/Lib Dem agreement to keep the Tories out, he said: “There will be no pact and there will be no deal.
“It’s great that political parties are campaigning to try and win people’s support. We’re fighting really hard to do that.”