BBC - Nigel Farage says he will resign as MP for Clacton and stand in the subsequent by-election, after facing intense scrutiny over financial support he has received.
The Reform UK leader said the "people of Clacton should be the judges of my actions", as he insisted he has done nothing wrong.
But the Conservatives, Labour, Restore Britain and the Lib Dems have ruled out standing candidates against him, in an effective boycott by his main opponents.
Farage has been under investigation from Parliament's standards commissioner since May after not declaring a £5m gift he received from a billionaire Reform donor before he became an MP.
Opposition parties have been calling for a further such probe, after it emerged he did not disclose support reportedly provided by a different political ally.
Farage claimed parliamentary standards investigations were "now being used as a political tool" and he did not want to be "judged" by the media, before announcing he would force a by-election in which he would stand.
In a live video statement released to the media by Reform, he said the by-election would give voters the chance to "stick two fingers up at the entire establishment".
But Labour has ruled out standing against him, with a spokesperson saying it would not "indulge" the Reform UK leader by standing a candidate "in this circus".
Tory leader Badenoch dismissed the by-election as a "gimmick", adding that Farage had called it to "distract people from what is happening".
She added her party would stand instead in a "real by-election" she hoped would be triggered in the wake of the standards investigation.
Farage's resignation will mean the ongoing investigation by the standards commissioner into the £5m gift is suspended. It will be resumed if Farage wins the by-election and returns to Parliament.
One possible outcome of a standards investigation is a suspension which triggers a recall petition. This process enables an MP to be removed and a by-election triggered if 10% of eligible registered voters sign a petition.
Farage resigns as MP for Clacton, triggering by-election which he says he will stand in
Farage used his speech to claim "the establishment" had turned to "foul means" to target Reform following the party's rise in popularity.
Changes to political donation rules and the government's decision to delay 30 local council elections in England - a decision it later reversed after a legal challenge from Reform - were among the issues cited by him.
He also said he spent the weekend thinking about his future after complaining about media treatment of his family, following the publication of a story by the Sunday Times on his links to longstanding ally George Cottrell.
The newspaper said Farage had received support ahead of the 2024 election from Cottrell, who was jailed for eight months in the US in 2017 after pleading guilty to a charge of wire fraud.
This reportedly included paying for staff who provided Farage's security and worked on his social media content. According to the newspaper, Farage also used a property near Buckingham Palace rented by Cottrell.
Scrutiny over Farage's finances first hit the headlines earlier this year, after it emerged he had received a £5m gift from Christopher Harborne, a Thailand-based British cryptocurrency investor, in April 2024, before he entered Parliament.
Harborne is one of the party's most important financial backers, having donated £15m to Reform since the start of last year.
Farage said the £5m gift was given on an "unconditional basis" and it was needed to help with his personal security in future.
His team has made a similar argument for why the "in kind" - non-cash - benefits allegedly from Cottrell were not registered.
"Let me be absolutely clear: I have done nothing wrong. I have not broken the law in any way at all. I have not misused public money," he added.
Parliament's rulebook says newly-elected MPs have to declare gifts or benefits, including accommodation, received in the 12 months before their election that relate to their "parliamentary or political activities".
There is an exemption for gift and benefits that are "purely personal".
'Vanity project'
Farage won Clacton at the 2024 general election, finishing 8,405 votes ahead of the Conservatives. He had previously been unsuccessful on his previous seven times standing to be an MP.
Farage's resignation will only be confirmed once the government has given him a crown appointment, the mechanism that disqualifies him from being an MP.
Liberal Democrat leader Sir Ed Davey called for the government to "block his resignation until the standards commissioner has finished investigating him".
"If this by-election does go ahead now, we are calling on all parties to stand aside and refuse to give oxygen to Farage's vanity project," he added.
Restore Britain leader Rupert Lowe said his party would not stand in the by-election triggered by Farage's resignation, but would if a by-election was ultimately triggered by the standards investigation.
A Green Party spokesperson said: "This is a decision for Clacton Green Party but we are a political party - we contest elections."
