Britain's ruling Conservative Party warned supporters on Friday that voting for Nigel Farage's Brexit Party could result in Britain's withdrawal from the EU being stopped and could put left-wing Labour Party leader Jeremy Corbyn into Number 10 through "the back door."
An email from Conservative Party Chairman James Cleverly said: "A vote for Farage risks letting Jeremy Corbyn into Downing Street via the back door."
"It will not get Brexit done - and it will create another gridlocked parliament that doesn’t work."
This follows an announcement by Nigel Farage on Friday that the Brexit Party would run in every seat across the UK at the 12 December general election, unless Boris Johnson drops his Brexit withdrawal agreement.
The Brexit Party leader issued a warning to Johnson that the Brexit Party would use the entire election campaign ensuring that every home is aware that his withdrawal agreement is a "sell out."
Mr Farage said "We will contest every single seat in England, Scotland and Wales. Please don't doubt that we are ready".
"Do not underestimate our determination or organisation".
The Brexit Party aims to challenge both Labour and the Conservatives, with Farage declaring that he has 500 parliamentary candidates ready to contest seats across the country.
Despite the comments, Farage has yet to reject the prospect of an election "pact" with the Conservatives entirely, instead telling Johnson that he has until 14 November to scrap his withdrawal agreement and instead pursue a "clean break" Brexit.
Mr Farage acknowledged that the "risk of the vote being split is very real", as he launched the Brexit Party's election campaign, despite previously saying that also he aims to target Labour heartlands seats in the north and the East Midlands which voted to leave.
Before the Brexit Party campaign, the Conservative Communities Secretary Robert Jenrick rebuked any notion of a pact with the Brexit Party while talking to the BBC, saying: "We are not interested in doing any pacts with the Brexit Party, or, indeed with anybody else."
"We are in this to win it," he added.
Trump Says Farage, Johnson Can Join to Become 'Unstoppable Force'
Farage's comments come a day after Nigel Farage conducted an interview with US President Donald Trump, who praised the British Prime Minister and attacked the Labour opposition.
He told Farage during the LBC interview "I have great relationships with many of the leaders, including Boris. He is a fantastic man and I think he is the exact right guy for the times and I know that you and him will end up doing something that could be terrific."
"If you and he get together, you know, unstoppable force and Corbyn would be so bad for your country."
"He would be so bad. He would take you in such a bad way. He would take you into such bad places."
He urged Farage and Johnson to join together saying "I wish you two guys could get together I think it would be a great thing."
The Brexit Party contesting seats against the ruling Conservatives could be electorally problematic for Boris Johnson as the party may split the Leave vote in key constituencies across the country, resulting in a victory for neither party and allowing either Labour or the Liberal Democrats to win the seat.
The Prime Minister has been adamant that he will fight his election campaign the basis of delivering his deal, seemingly ending any possibility of a Brexit pact.
Boris Johnson last week reneged on earlier pledges to leave the EU by the 31 October deadline, requesting instead an extension to the withdrawal process to the end of January.