The leader of Reform UK, Richard Tice, has offered a “cast-iron guarantee” the party will put up a candidate against every Conservative in the next general election, ruling out a 2019-style deal even if the Tories back some of his policies. After a speech to relaunch the party, which was level with the Liberal Democrats in some recent polls, Tice said Reform UK already had 600 candidates in place and would stand in every seat outside Northern Ireland. “Absolutely not,” he told the Guardian when asked if the party could potentially stand aside for Tory candidates who explicitly backed the party’s low-tax policy platform. “It’s a 110%, cast-iron guarantee. We’ve already got 600 candidates, we will stand everywhere. “I think people are starting to realise that we’re serious about this. For obvious reasons, some people have ignored us until now, but we’ve got momentum. We’re equal or above the Lib Dems.” The commitment will add to Rishi Sunak’s political woes and could make a Conservative defeat in the general election, expected next year, more likely. In 2019, what was then the Brexit party greatly boosted Boris Johnson’s chances by standing aside in more than 300 Tory-held seats after he gave commitments on a hard Brexit. While Tice’s party is unlikely to win a seat in the next election, if it were to take up to 8% of votes, as polling indicates it could, the bulk of these would come from disgruntled Conservative voters, a demographic the relaunch squarely targeted. Tory MPs might be more nervous still if Nigel Farage, who led the party until March 2021, returned as leader. But Tice said this would not happen, and that Farage would remain focused on his media career. “He’s done that,” Tice said when asked if Farage might take the helm again. “He’s very much enjoying what he’s doing. I speak to him two or three times a week. He’s on his own really good form and he’s massively supportive of everything that we’re doing.” Tice’s speech, at a hotel in central London, focused on policies the party has advocated for some time, including an increase in the starting rate for income tax from £12,570 to £20,000, efforts to get people off out-of-work benefits, and policies to assist the NHS, including a period in which frontline staff would pay no income tax. The costs – Reform UK say the income tax threshold plan would cost £40bn a year – would be recouped through moving people off benefits and cutting government waste, Tice said. Speaking afterwards, he said the income tax cut would be “the fastest, most dramatic way to help people on the lowest incomes”. “I’ve been talking about it for 20-odd months, but for obvious reasons people have sort of ignored us until suddenly we’ve appeared as having momentum,” he added. Dismissing Labour as being devoid of ideas, Tice pointed to a newspaper column last week by the Tory peer David Frost urging Conservatives “to fight for the party and not be tempted by a Reform UK vote”, as a sign the government was alarmed. “You know the Tories are worried when they’re writing in newspapers ‘please don’t vote Reform’,” he said.