Nigel Farage is claiming Reform UK is now the Opposition to the Labour government after a string of polls put them ahead of the Tories.
He also ruled out a pact with the Conservatives as he launched a new attack on their leader Kemi Badenoch.
The Conservatives have 121 MPs at Westminster, compared to Reform’s five.
But Ms Badenoch, after 100 days as Tory leader, has seen her party fall behind Reform in a series of polls, which has even overtaken Labour in at least one survey and is gaining town hall seats.
“We are now the opposition to the Labour government and I think the Tories’ days, frankly, are numbered,” Mr Farage claimed.
Speaking at a Farmers To Action event in north London, he added: “I think we’re the ones providing the challenge. We’re the ones out doing stuff every day. We may only have five MPs, but boy, they’re certainly being felt in Westminster, and the Labour Party doesn’t know what it is anymore.
“And frankly, today’s the 100th day of Kemi Badenoch’s leadership - it doesn’t stand for anything.”
Mr Farage, one of the key architects of Brexit which is widely seen to have been a failure which has damaged the UK economy, also called for inheritance tax to be abolished but did not explain how such a move should be funded.
A new poll suggested many Britons are yet to make up their mind about Ms Badenoch.
After three months in office, 25% say she is doing a good job as leader of the Conservatives, 33% a bad job, and 42% “don’t know”.
Mr Farage flatly denied that he would strike a deal with the Tories.
Asked if there is any truth in reports claiming that Reform UK is looking at an alliance with the Conservatives, he said: “Absolutely none whatsoever. No, none.“
A survey by Ipsos, five years after Britain quit the European Union, found more Britons blame Boris Johnson for the failures of Brexit than Mr Farage.
Ms Badenoch has sought to avoid rushing into announcing new policies, insisting that the Tories need to admit their mistakes and undergo broader changes.
But her stance has risked leaving the Government and Reform more political space to make their cases to voters.
The Conservatives are not opposing a third runway at Heathrow, highlighting its potential to boost economic growth, however, shadow transport secretary Gareth Bacon has warned the development faces “major obstacles”.
