Farage is one of Britain's most recognisable politicians best known for his decades-long - and eventually successful - crusade for Britain to leave the European Union. His Reform UK party began life as the Brexit Party in 2018, during the tortuous negotiations over how Britain would leave the bloc.
Farage's return to frontline politics has split support among right-of-centre voters, further damaging Sunak's hopes of winning an election he was already predicted to lose to the opposition Labour Party.
Prime Minister Rishi Sunak met with Pope Francis at the G7 summit in Italy. (AP PHOTO)
That impact was shown in a YouGov poll on Thursday that put Reform UK on 19 per cent, up from 17 per cent previously, and the Conservative Party unchanged on 18 per cent. Labour, led by Keir Starmer, topped the poll with 37 per cent.
"If this poll was replicated it would hand a blank cheque to Labour," Sunak said in Italy, where he is attending the G7 summit, according to remarks reported by British media.
"Ultimately a vote for anyone who is not a Conservative candidate makes it more likely that Keir Starmer is in No10."
Farage said his party had made a "phenomenal" start to the campaign and was now the real opposition to Starmer's Labour.
Keir Starmer's Labour Party is tipped to win when Britain goes to the polls on July 4. (AP PHOTO)
He predicted that Reform's result would top the four million votes won by his previous political party, UKIP, in the 2015 election.
"I genuinely think we can get over six million votes. I don't know where the ceiling is," he told a press conference on Friday.
In 2019, the Conservatives won 14 million votes while Labour took 10 million.
But in Britain's first-past-the-post electoral system, winning millions of votes across the country does not necessarily translate into winning any of parliament's 650 individual constituencies.
Labour said Farage, who has stood unsuccessfully for parliament seven times, had never been tested on delivering the changes he called for, but should not be underestimated.
"In terms of Labour versus Reform, we're going to take them on. We're going to take them on in the battle of ideas and the battle of arguments," Labour's health policy chief Wes Streeting told Sky News.
Other opinion polls show the Conservatives much further ahead of Reform, but most still show a rise in support for the party since Farage took over.
"However one looks at it - although it may not be the case that Reform are ahead ... on average they might still be about four or five points behind - this is still bad news for the Conservatives," polling expert John Curtice told the BBC.
Farage did not set a target for the number of seats he wanted to win, calling the first-past-the-post system "outdated".
Reform's support is spread comparatively evenly across the country, whereas backing for the larger and more established parties is more concentrated by geographic areas, meaning it may not win many seats at all.
"Whatever we do, we may not get the number of seats we deserve," he said.Â
"But are we going to win seats in parliament? Yes. How many? ... we've got momentum behind us and there's three long weeks to go."
