Nigel Farage, who helped champion Britain’s departure from the European Union, will stand as a candidate in next month’s election and will lead the populist Reform Party – in a major blow to Prime Minister Rishi Sunak.

The surprise U-turn by Farage, now a TV host, will boost his movement’s profile and challenge Sunak’s Conservatives for the support of voters at a time when the governing party is already badly trailing the Labour Party in the polls.

Farage, 60, had previously said he would not stand in the July 4 vote so that he could instead help Donald Trump fight the US election later this year.

“I’ve changed my mind,” he said.

“It’s allowed you know, it’s not always a sign of weakness. It could potentially be a sign of strength.”

Farage will also take over as leader of Reform, replacing Richard Tice. He said on Monday (local time) he felt guilty not standing up for people who had become disillusioned with politics and had always backed him.

“We are going to be the voice of opposition, and I tell you what, I have done it before, I’ll do it again, I’ll surprise everybody,” he said, adding it was a fait accompli that Labour would win but that he wanted to position Reform as its main opponent.

He said he would lead a “political revolt” in Britain because “nothing in this country works anymore”, citing problems with public services such as healthcare and roads.

Farage will stand in the parliamentary seat in Clacton, Essex, a resort town in eastern England that overwhelming voted for Brexit in the 2016 referendum.

Although Farage has stood unsuccessfully for parliament seven times, he is still one of the most influential British politicians of his generation, putting pressure on a succession of prime ministers to take tougher positions on the EU and on tackling immigration.

Shunned by the political establishment and backed by eurosceptic financiers, Farage helped sell Brexit to millions of voters in England and Wales who felt ignored by the main Conservative and Labour parties.

Although he was educated at an expensive school and worked as a commodities trader, Farage – who has survived testicular cancer and a plane crash – has cultivated an image of an anti-establishment figure.

He is routinely pictured with a cigarette in one hand and a pint of beer in the other.

Before Farage took the stage on Monday, Tice said the party wanted a way to “turn on the rocket boosters” to the election campaign.

Divisive and charismatic, Farage has previously made comments that his political opponents have called racist.

He appeared in front of a poster during the Brexit campaign showing lines of migrants under the slogan “Breaking Point” and last month said some Muslims did not share British values.

At the last general election in 2019, Farage’s party decided not to contest seats held by the Conservatives, then led by Boris Johnson, to avoid splitting the pro-Brexit vote.

Polls suggest the opposition Labour Party is on course for victory on July 4, with the Conservatives staring at one of the worst results in their history.

Support for Reform runs at about 10 per cent across Britain, giving the party the third highest vote share, polls suggest.

But under Britain’s winner-takes-all system, the party had not been expected to win any seats.

A poll earlier this year forecast the Conservatives would win Clacton with Reform coming third.

One betting company said Farage had a 40 per cent chance of winning the seat after his announcement.

Under pressure, Sunak has already tried to win over voters tempted by Reform with policies such as tax cuts for pensioners, the reintroduction of national service and his plan to send illegal asylum seekers to Rwanda.

Asked on Monday if he was worried about Farage entering the contest, Sunak said a vote for Reform would help Labour.

-with AAP