The party’s interim leader will be Gerard Batten, a member of Parliament and a founder of the party, known as UKIP. In a blog post after the 2017 terrorist attack at Westminster, Mr. Batten described Islam as “a death cult, born and steeped in fourteen hundred years of violence and bloodshed.”
In an interview, Mr. Bolton said UKIP had struggled to hold together after winning the Brexit vote — he described ideological positions ranging from “far right wing, libertarian, to anarchistic, rejecting all authority” — and held out scant hope for the party’s regaining relevance.
“I don’t think UKIP will disappear,” he said. “The question is: Will it have any influence on how we leave the European Union and chart the future course of the country? I think it will struggle.”
For years, the UKIP leader Nigel Farage made the case that Britain could not claim full sovereignty or control immigration unless it exited the European Union. The message resonated with many British voters and unnerved Conservative legislators, who feared UKIP would hurt them the 2015 election.
In the end, UKIP won 13 percent of the vote, but received only one seat — a disappointment compensated by Prime Minister David Cameron’s pledge to hold a referendum. Britons voted to leave, 52 percent to 48 percent. In the wake of that victory, its main funder, Arron Banks, hoped to reshape UKIP to attract disaffected Labour voters, an effort that has borne little fruit.
Tony Travers, a professor in the government department of the London School of Economics, said the party could be reinvigorated if voters were keenly disappointed by Brexit, or if Mr. Farage returned as leader.
“You cannot get away from the fact that they have made the weather, politically, on two issues, on forcing the referendum and on the question of migration,” he said. “They’ve had more of an influence than you would expect from a party that only won one parliamentary election.”