Nigel Farage has launched a blistering attack on Conservative leader Kemi Badenoch, declaring her accusation of fraud against him "absolutely disgusting".
The Reform UK leader responded furiously to claims that his party had "fabricated" its membership numbers.
Farage threw down the gauntlet to the Conservative Party, offering to have Reform UK's membership numbers independently verified.
The heated exchange erupted after Reform UK claimed its membership had surpassed the Conservative Party's numbers on Boxing Day.
"We, even since we went through that number yesterday morning, the numbers are rocketing where another five or six thousand higher than we were when we went past the Conservative Party.
"I know that Kemi Badenoch is well known for her aggression and for lashing out, but to accuse me of not understanding the digital age when I've got 5.5 million followers on social media and she's got fewer than a third of a million, frankly, was a bit rich.
"I'm sorry, the truth is there is a massive shift going on in British politics."
He added: "If the Conservative Party want us to call in one of the big four auditors to check the validity of our numbers against the ballot papers that were sent out at the leadership contest, thousands of which went to lapsed Conservatives.
Conservative leader Kemi Badenoch hit back
KEMI BADENOCH
The row began when Reform UK projected its membership figures onto Conservative Campaign Headquarters in London overnight. A digital counter on Reform's website showed the party's membership ticking past 131,680 - the figure declared by the Conservative Party during its leadership election earlier this year.
Farage called it a "historic moment", declaring: "The youngest political party in British politics has just overtaken the oldest political party in the world."
"Reform UK are now the real opposition," he added.
The official Reform X account later posted what it described as a "screenshot of our internal membership numbers", appearing to show figures exceeding 134,000.
Badenoch swiftly dismissed Reform's membership claims as "fakery" in a series of posts on X.
"It's not real. It's a fake clock coded to tick up automatically. We've been watching the back end for days," she wrote.
The Conservative leader accused Farage of manipulating supporters at Christmas.
"Farage doesn't understand the digital age. This kind of fakery gets found out pretty quickly, although not before many are fooled," she added.