Nigel Farage’s Reform party has overtaken the Conservatives in a poll for the first time.
The Tories were pushed into third in the survey, by pollsters YouGov.
The findings will come as a blow to Rishi Sunak after a disastrous election campaign and risks triggering panic among many Tory MPs.
The poll results were released minutes before Mr Farage was due to take part in a 7-way debate on ITV, with Conservative cabinet minister Penny Mordaunt, among others.
As the TV showdown opened he told millions of viewers “we are now the opposition to Labour”.
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The poll found support for Reform had increased by two points to 19 per cent while the Tories were unchanged on 18 per cent.
Labour was still in the lead on 37, while the Liberal Democrats were down one point at 14 per cent, according to the survey for The Times.
Earlier Mr Farage suggested the Conservative Party “may well be dead, this may well be the end of their journey”.
He also indicated that his political roles model is Canada’s Stephen Harper, who orchestrated a merger between Reform and their Conservative rivals to unite the right.
Because of the first-past-the-post system, Mr Farage’s party is still unlikely to take any more than a handful of seats at Westminster.
But overtaking the Tories in a poll will be seen as a hugely symbolic moment for Rishi Sunak’s party.
Many Tory MPs are terrified Reform will put the final nail in their coffin, not by winning their seat but by taking enough votes to hand it to Labour or the Lib Dems.
Reform also claimed they had made history when they unveiled a Party Election Broadcast that turned TV screens black for nearly five minutes – except for the message: “Britain is broken. Britain needs Reform.”
Mr Sunak has infuriated his own MPs as he has presided over what has been seen as a disastrous election campaign.
At the weekend he was accused of going into hiding after he was forced to make a grovelling apology for leaving the D-Day commemorations early to take part in a TV interview.
Mr Sunak was also ridiculed for claiming his family had had to go without Sky TV when he was a child.
Mr Farage has mocked the prime minister after a Tory candidate used pictures of him on her leaflets.
The arch-Brexiteer is plastered across the leaflets of right-wing Conservative Dame Andrea Jenkyns.
Mr Sunak, meanwhile, is nowhere to be seen, and there is no reference to the Conservative Party or use of any of its branding.
Reform has had its own troubles in this election, however.
Earlier this week Mr Farage pulled out of a high-profile BBC interview as his Reform party faced a row over whether the UK should have appeased Hitler.
The former Ukip leader was due to take part in a Panorama special with Nick Robinson, which was due to be broadcast on Tuesday night.
But it was yanked from the schedules and postponed, despite Mr Farage continuing to campaign in Barnsley and Nottinghamshire.
A poll by YouGov earlier this week put Reform just a point behind the Conservatives, who had fallen to 18 per cent.
But other surveys by different pollsters have suggested the gap between the two parties is larger.