Robert Jenrick has told Conservative members there will be no deal with Nigel Farage if he is elected party leader to replace Rishi Sunak.
The former Home Secretary, who resigned after saying Sunak was not strong enough during the deportation flights to Rwanda, is the leading right-wing candidate in the leadership race.
At a rally in Upminster, Essex this week, Jenrick told party members he plans to win back Conservative voters who have defected to Farage's reform proposal.
But unlike her right-wing colleague Suella Braverman – who leads the party in support but has struggled to find enough MPs to nominate her – Jenrick said there would be no deal with Farage.
In June, Ms Braverman suggested the Conservatives should welcome Mr Farage into the party, as there was not much difference between the Tories and the Reform Party.
Jenrick's rejection came after it emerged that Reform is primarily concerned about his nomination and hopes his rival Tom Tugendhat, who is more associated with the party's centrist One Nation members, will win instead.
A number of sources have claimed that former Conservative MP and now Reform Party MP Lee Anderson said Jenrick would “cause the biggest problem”.
Mr Anderson denied this and said The independent: “None of them worry us. Just look at their majorities.”
However, Tugendhat's allies believe he can follow in David Cameron's footsteps in the leadership election, claiming he can win the leadership race by establishing himself as the favourite at the party conference.
The former Prime Minister, now Lord Cameron, was the surprise winner of the race in 2005 despite starting behind the bookmakers' favourite, David Davis.
But a speech he gave without notes at a party meeting that year, which would make him a star, changed his electoral chances.
As standard-bearer for One Nation's Conservative MPs, Tugendhat could still struggle to win over more right-leaning Conservative members if he makes it to the final two.
An ally of Mr Tugendhat said: “One thing people misunderstand about the membership is how much they want to win power. Yes, they are more to the right at the moment. But what they will be looking for is a candidate who can win and who can ensure that they are back in No 10 sooner rather than later.
“They also realise they made a mistake with Liz Truss and are determined not to do it again. They will be looking for a winner and whoever emerges as that person – as David Cameron did.”
Mrs Truss was prime minister for less than two months before being ousted by her own MPs. She was replaced by Rishi Sunak, but he announced his intention to step down as leader after a disastrous result in the general election earlier this month.
He will remain as interim leader while the party spends the next four months selecting his successor.
Mr Tugendhat and Mr Jenrick have both secured the support needed to progress to the next stage before nominations close on Monday afternoon. Former Home Secretary James Cleverly has also secured the necessary nominations, as has former Jobs and Pensions Secretary Mel Stride.
Former Business Secretary Kemi Badenoch, who has accused her rivals of misleading her, and another former Home Secretary, Dame Priti Patel, are also expected to be on the ballot paper.
Members of Parliament will narrow down the list of candidates to the final two, after which party members will be allowed to vote.
But before that, there will be a “beauty parade” at the annual party congress, where the candidates will try to profile themselves as favorites for the position.
