Downing Street has categorically ruled out any kind of electoral pact with Nigel Farage and the Brexit Party.
Mr Farage had offered Boris Johnson a deal for the two parties to secure a huge pro-Brexit majority at a future general election if the PM opted for a “clean-break Brexit”.
But Number 10 said the Prime Minister would not do a deal with the Brexit Party leader.
A senior Conservative source described Mr Farage and Brexit-campaigning ally Aaron Banks as not being "fit and proper", and said they should never be "allowed anywhere near" government.
A Number 10 spokesman said: "The PM will not be doing a deal with Nigel Farage."
The senior Conservative source added: "Neither Nigel Farage or Aaron Banks are fit and proper persons, and they should never be allowed anywhere near government."
Polls show the Conservative Party taking a lead, but with support still holding for the Brexit Party, it is thought the Tories may still struggle to secure a big majority.
Mr Farage, who led his party to victory in the Euro elections this year, reportedly offered not to field candidates against sitting Tory MPs or in seats that are being targeted by the Tories.
The Brexit Party have taken out a full wraparound advert on the front page of the Daily Express this morning offering Boris Johnson an election pact. Fair to say they are not messing about pic.twitter.com/I21nrHYbe9
— Jack Blanchard (@Jack_Blanchard_) September 11, 2019
In return, Mr Farage wants a clear run at traditional northern Labour seats that saw successes for Ukip in the past, according to The Sun.
A source told the paper: “It's very simple, it's all about the numbers. Boris knows he cannot win a majority without our help.”
The source added that Mr Farage “has had some conversations with people who are very close to Boris” in order to “scope out whether he's serious about a deal than actual negotiations”.
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The Brexit Party also sent out a tweet offering an “election offer” to the PM, vowing to “destroy Corbyn’s Labour” if a no-deal Brexit is secured.
Meanwhile, the Prime Minister has sought to shore up support for his Brexit ambitions by holding talks with the Conservatives' key parliamentary allies the DUP, with leader Arlene Foster and her deputy Nigel Dodds spending more than an hour inside Downing Street.
Mrs Foster said the PM had demonstrated his "commitment to securing a deal which works for the entire United Kingdom" as well as the Republic of Ireland, including rejecting the idea of a Northern Ireland-only backstop – which would have created a special economic zone for the country.
The Conservatives have enjoyed the support of the DUP's 10 MPs on many key issues since June 2017, although Theresa May was unable to convince them to vote for her Brexit deal.
Over in Labour, deputy leader Tom Watson is set to call for a second referendum before an election – putting him at odds with Jeremy Corbyn, who has outlined his desire for an election before a referendum.
A ComRes poll for the Daily Telegraph suggested 43% of voters believe the UK should leave without a deal on October 31 if the EU refuses to make any more concessions, compared with 32% who disagree and 25% who answered "don't know”.
But 46% agreed they are "fearful" of the consequences of a no-deal Brexit, while 33% disagreed and 21% answered "don't know”.
The poll was conducted between September 6 and 8, with 2,016 British adults surveyed.