The Conservative party of British Prime Minister Rishi Sunak has fallen behind the anti-immigration Reform UK party for the first time in a poll by YouGov, which called the development a "seismic shift".

The new poll, conducted on Wednesday and Thursday, shows Brexiteer Nigel Farage's Reform with 19 percent support going into national elections next month, compared to the Conservatives' 18 percent. Both are trailing far behind the Labour party.

YouGov noted it was "worth keeping sight of the fact that these figures are well within the margin of error of one another -- we will not be able to tell for some time whether Reform can sustain or improve their position relative to the Conservatives".

Still, it added: "The fact that Nigel Farage's party are neck and neck with the governing Conservatives is a seismic shift in the voting landscape."

The poll showed the Labour party, led by Keir Starmer, still in a commanding lead at 37 percent.

Given the hefty and sustained polling lead, Starmer is widely expected to become the next prime minister, but he is fighting to overcome persistent Tory claims that his party will recklessly spend public finances and increase personal taxes.

Right-wing firebrand Farage said his party was "now the opposition to Labour" in a debate appearance on ITV Thursday evening.

After 14 years in power, the Conservatives are firmly on the back foot following an unprecedented period of political upheaval, with five Tory prime ministers since 2010, and three in just four months in 2022.

Much of that was the result of Brexit, the country's tortuous departure from the European Union.

But there were also self-inflicted wounds such as Liz Truss's short-lived tenure, when her unfunded tax cuts spooked the markets and crashed the pound.

Labour's Starmer is campaigning on promises to spur growth and restore economic "stability".