The Conservatives plan to intensify their attacks on Reform’s economic policy as they gear up for a fight to the death between the two big parties of the right, a battle brought to new levels of acrimony by Robert Jenrick’s defection.

While Jenrick, the former shadow justice secretary, insisted he was “uniting the right” in signing up to Reform, Kemi Badenoch portrayed her former colleague as dishonest and no loss to the Conservatives, saying: “Nigel Farage is doing my spring cleaning for me.”

In a blistering TV interview of his own, Jenrick castigated Badenoch’s Conservatives, saying that the “arsonists” who tanked its reputation were still in charge.

While it remains to be seen whether any other sitting Tory MPs will follow Jenrick, the open rancour makes it extremely unlikely that a Badenoch-led Conservatives would do a deal with Reform, pitting the parties against each other in a fight for votes that will start with May’s elections in Scotland and Wales and for English councils.

The Conservatives remain well behind Reform in national polling, but Badenoch and her team hope a gradual shift in voter attention from migration to the economy will help her party, with a recent internal Tory strategy meeting focused on the party’s economic message.

Internal Conservative polling suggests that economic policy is a key weakness for Reform, along with the sense that the party is a one-man band.

After a dramatic day on Thursday in which Jenrick was forced to hastily seal his move to Reform after Badenoch’s team learned of his plans and removed him from his shadow ministerial job and the party whip, he went on the offensive on Friday with a BBC interview castigating his old party.

He said: “I came to the conclusion over the course of the last year or so that … the party hadn’t changed, that the people who’d made those mistakes were still sat around the shadow cabinet table, the arsonists were still in control of the party, and that this was not a party that was capable of even understanding what it had got wrong, let alone fixing it.”

Asked if he risked splitting the UK’s political right with the move, he replied: “This is uniting the right. My message to millions of people in the country who stuck with the Conservative party, often with gritted teeth … if you want to get rid of this Labour government and have a strong reforming government to fix the country, there’s frankly only one way to do that.”

In her own interviews during a visit to Scotland, Badenoch was equally blunt about her former shadow cabinet colleague and his new party. Asked if she could commit to the Conservatives going into the next election as a solo force, she said: “Yes. How do you do a deal with liars?”

On Jenrick, Badenoch said: “You can’t believe a word that comes out of his mouth. This is a man who was asked yesterday morning, ‘Are you going to defect?’ And he said ‘never’ to the chief whip.”

She added: “People from Reform and other Conservative party members have been bringing stuff to me about the actions he had been doing to undermine the party, and I kept giving him a chance. So I’m just glad that Nigel Farage is doing my spring cleaning for me. He’s taking away my problems.”

Badenoch urged any Tory MPs considering a similar move to act quickly: “If they’re people who do not belong in our party, who think that it’s all a game and that people’s lives are a game, they just want all this psychodrama, then yes, they should go. We don’t want people like that in the Conservative party.”

Jenrick has urged other rightwingers to follow his example, writing in the Telegraph on Friday: “If you’re not already onboard, join the movement. The future of the country is on the line.”

He told the BBC, however, that he did not know of any other imminent high-profile defections.

Some Conservative MPs said that Jenrick’s brutal defenestration by Badenoch was likely to have made others more wary, and that the party was determined to unite. “It was all about Robert and his ambition, and he needed to grow up,” one said. “Everyone is sick of this crap.”

Speaking to Sky News, Nick Timothy, who has been given Jenrick’s job as shadow justice secretary, said voters would not welcome his former colleague’s move.

“The country is absolutely sick of the backbiting, the backstabbing and, frankly, the lack of seriousness with which lots of politicians have taken the very serious and significant challenges that the country faces,” he said.