It started as a classic piece of political theater from a master of the craft, Nigel Farage, leader of the right-wing populist party Reform U.K. and the most famous insurgent of British public life.

After weeks of pressure over revelations about his finances, Mr. Farage abruptly announced on Tuesday that he would resign his parliamentary seat in Clacton, east England, and run there again, seeking a vote of confidence from electors in an area where his support is strong.

“I’ve decided that the people of Clacton should be the judges of my actions,” he said in a grievance-filled speech that was livestreamed on Reform’s social media channels. He appeared to calculate that the vote would short-circuit an ongoing investigation into whether he broke parliamentary rules by not disclosing a gift of 5 million pounds (about $6.7 million) and would show that voters did not care about the inquiry’s outcome.

“This will be a people-versus-the-establishment by-election,” he said.

Within hours, it appeared that the gambit was turning to farce. All the main political parties announced that they would boycott a contest they see as a self-serving gimmick.

By Wednesday morning, it seemed likely that Mr. Farage’s main adversary would be a comedian and novelty candidate who calls himself Count Binface and wears a trash-can-themed costume. Britain has a rich history of joke contenders running in special parliamentary elections, but in this one, Count Binface (whose real name is Jon Harvey) may get more attention than usual.

“It does seem as if what looked like a masterstroke has turned into a dud,” said Tim Bale, a professor of politics at Queen Mary University of London.

It was, he said a “pretty obvious response from the other parties to what is essentially a stunt intended to lure them into a contest, which would have allowed Farage to portray himself as a victim of an establishment stitch-up. They have refused to do that.”

On Wednesday, Zia Yusuf, who speaks for Reform on home affairs, reposted on social media a statement that “the establishment is terrified of voters in Clacton.” Sarah Pochin, a Reform lawmaker, said that the Conservative Party, which held the seat until Mr. Farage won it in 2024, was so scared of losing to him there that it dared not run a candidate.

The political convulsions come as Mr. Farage’s party has suffered some rare electoral setbacks after leading in opinion polls for more than a year. While it performed exceptionally well in municipal elections in May, the party has lost three special parliamentary elections in the past year where it had prospects of winning. And Reform’s lead position in national polls, which has fallen to about 25 percent from about 30 percent last year, has drawn more scrutiny to Mr. Farage.

The £5 million gift came to light as a result of an investigation by The Guardian, which revealed in April that Mr. Farage had received the money from a cryptocurrency billionaire, Christopher Harborne, a Briton who lives in Thailand. The gift was received weeks before Mr. Farage unexpectedly announced he would run in the 2024 general election.

Because the money was given before he entered Parliament, Mr. Farage argues that there was no requirement on him to declare it. But parliamentary rules state that new lawmakers must declare any financial benefits received in the 12 months before their election that might “reasonably be thought by others to influence his or her actions, speeches or votes in Parliament, or actions taken in his or her capacity as a member of Parliament.” As a result, Parliament’s standards commissioner, Daniel Greenberg, is investigating whether Mr. Farage broke the rules by not including the gift in his declaration of interests.

In recent weeks, there have been signs that the Reform leader has been increasingly rattled by the scrutiny of his financial affairs. In one interview with “BBC Breakfast” last month, Mr. Farage became visibly angry as the host asked him how much of it he had spent and whether he regretted not declaring it. “It’s an unconditional gift. I can spend it on cars if I want to,” he said, adding, “It’s literally none of your business.” In an interview with LBC, he said, “I can spend it on Ferraris if I want,” adding: “I can do what I want with it. I can put it on the horses.”

Last weekend, The Sunday Times of London reported that Mr. Farage had separately failed to declare benefits provided by a close ally, George Cottrell, who served eight months in prison in the United States after being convicted of wire fraud.

Mr. Cottrell’s support included providing a social media staff that worked for Mr. Farage in the months before he was elected, The Sunday Times reported, as well as the use of a property rented by Mr. Cottrell near Buckingham Palace.

Mr. Farage insists he followed all of the rules and has accused journalists of hounding his family, but on Tuesday he confirmed that Mr. Greenberg was also looking into the case concerning Mr. Cottrell.

If the investigation rules against Mr. Farage, he could be suspended from Parliament and potentially forced to put himself up for re-election in Clacton.

The announcement of his resignation on Tuesday appeared designed to pre-empt that prospect and seize control of the political narrative. It would not block the investigation, however, which could be suspended pending the special election in Clacton and then resume if Mr. Farage won. This raises the possibility that the Reform U.K. leader could be forced into a second contest there later in the year.

Nonetheless, Mr. Farage is highly likely to win in Clacton, assuming the special election takes place as expected. On Wednesday, the country’s top financial official, Rachel Reeves, who has to authorize the resignation of a lawmaker using an obscure parliamentary rule, said she would do so even though she described this case as “a farce and a desperate distraction.”

Before the 2024 general election, Mr. Farage dominated the contest in the area, bustling down the main street, dropping into local pubs and, on one occasion, arriving to address supporters near a seaside pier in an armored vehicle.

By repeating those sorts of tactics, he sensed an opportunity to wrest back political momentum. But Britain’s great political disrupter may find that his hoped-for battle with “the establishment” will be fought against Count Binface, who, when interviewed by the BBC on Wednesday morning, gave a short response when asked how he would appeal to the people of Clacton.

“I’m not Nigel Farage,” he said.