Nigel Farage’s Reform is proving to be an “utter disaster” for the Conservatives, Professor Sir John Curtice has said.

The polling guru said the rise of the Brexiteer’s party had been “the most important development” in the election campaign so far.

Last night a bombshell poll put Reform ahead of the Tories.

YouGov found that 19% of voters were ready to support Mr Farage and his his candidates, while Rishi Sunak’s party were on 18%.

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After the poll was released Mr Farage, taking part in a seven way debate on ITV, declared: “We are now the real opposition to Labour.”

The fieldwork for the survey, undertaken for The Times, was carried out after the Prime Minister published his manifesto.

Sir John said an average of recent polls shows backing for Reform is now at about 15% or 16%.

Speaking at an online event organised by the Fraser of Allander economic think tank at Strathclyde, he said: “This is a real, real problem for the Conservatives because virtually all the people who are switching to Reform are 2019 Conservative voters.

“We also know from what happened in the local elections down south at the beginning of last month that if Reform were not on the ballot paper they wouldn’t be voting Labour instead.

“Any chance the Conservatives ever had when they fired the starting gun on May 22 that they might be able to narrow Labour’s lead was predicated on them being able to win back those Reform voters.”

Sir John said Mr Farage’s unexpected decision to stand in the election and take over the leadership of Reform had boosted the party in the polls.

“Basically rather than the Conservatives recovering during this campaign… you can see they are now four points lower than they were.”

He went on to say that Labour is “also losing ground”, but the lead Sir Keir Starmer’s party has over the Tories remains around 20 to 21 points “because both parties are losing grounds”.

He said Labour’s potential victory could be significant.

“We at the moment are looking at swings of 15%, 16% from Conservative to Labour.

“We’ve never had a swing of that size before. We could be having the biggest swing in the post-war era from one party to another.”

Sir John said the Tories and Labour “trying to knock chunks out of each other” was “probably helping the small parties out a wee bit.”

“The Liberal Democrats have started to rise in the polls. It is possible that the Liberal Democrats are finally reclaiming some of their lost votes to Labour,” he added.

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Meanwhile, Mr Farage has demanded a spot on BBC Question Time’s four-way leaders’ special.

Fiona Bruce is due to host interviews with Mr Sunak, Sir Keir, Sir Ed Davey and John Swinney on Thursday night.

“I think we can demand of right now that the BBC put us into that debate,” Mr Farage said during a press conference in central London.

“I would also very much like to do a debate head-to-head with Keir Starmer and the reason’s very simple – we think this should be the immigration election.”

Asked if he would join the Tories, the Reform UK leader said: “No, they’re done. The brand’s done.”

He added some Conservative voters from 2019 are “so disgusted with the political system, they feel absolutely betrayed by the promises that were made in 2019. The Conservative Party will not be in power for a decade, maybe more”.

Mr Farage said: “You know, you could say to me, ‘look, they’ve been around for 190 years’, but occasionally these big seismic shifts do happen. It happened in Britain in the 1920s, it happened in Canada in the early 1990s.

“I think this may well be one of those big 50 or 100 year-events that happens even under first-past-the-post politics. If we were in PR (proportional representation) we would be talking a very, very different game.”

Taking a question about whether Reform UK could “unite the right against Labour” during the next parliament, Mr Farage said: “Oh, I think so, yes.

“Who knows how many Tory MPs that are going to be there anyway? The number could be very small.

“The other problem they’ve got – and you’ve seen this in the polls in the last week – is the Liberal Democrats are on the rise and that reflects tactical voting that is going on certainly in southern central, southern and south west of England, so who’s to say how many MPs the Conservatives are even going to have?

“But, look, you know, if Damian Green and the Jeremy Hunt wing want to go and join the Liberal Democrats, I’d have thought they would be very, very at home there.”

Asked whether his party was in a position to capitalise on its rising support, the leader said: “Not really, no.

“I mean, look, we are not as organised and developed as the Liberal Democrats. They are very, very good at their ground game, they’ve got a network of councillors they’ve built up across the country.

“We’re honest with you, we admit we are not in that position. So, the way that we do it … the only way we can do this is we have to get the total number of votes well up over that six million figure, and if we do that we will start to break through with seats.

“So, is there a ground game for us? Yes. Are people now coming forward enthusiastically to help us? Yes. Are people coming forward and giving us 25 quid or more to join the party or support the party? Yes. Money is flowing in through the door, support and help is coming in.”

He added: “I’d have loved six months of this. We haven’t got six months, we’ve got three more weeks.

“We’re making the best of what we can, but I do think there’s a very, very big gap in the electoral market out there.”