Nigel Farage has claimed that Brexit party candidates have been “hounded and bombarded in the most extraordinary way”, complaining that “the tone of politics has deteriorated hugely” over the course of the election campaign.

Speaking the day before the country goes to the polls, the Brexit party leader said the campaign had been “very, very nasty” and that he was surprised his candidates had been able to withstand the abuse they had been subjected to.

“I’ve seen people who want to put themselves forward for election, which of course is our right in a free society, [be] hounded and bombarded in the most extraordinary way,” he said.

Farage was speaking to a gathering of activists in the constituency of Doncaster Central, after a major poll – produced using a method that accurately predicted the last election – forecast the Conservatives winning a majority of 28, within the margin of error, and the Brexit party winning no seats.

The party’s campaign has been dogged by criticism by campaigners and its own MEPs who say that standing candidates against the Conservatives risks splitting the leave vote. Catherine Blaiklock, the Brexit party’s founder who resigned after retweeting Islamophobic messages, said on Tuesday that Farage’s strategy had failed and that people should vote Tory.

Surjit Singh Duhre, the Brexit party candidate in Doncaster Central, has reported receiving a death threat and being driven off the road. The party has criticised the police for saying they were not treating the latter incident as suspicious.

Farage said that part of the reason for the number of abusive messages sent to Brexit party candidates was a Daily Mail front-page article that published their email addresses and called on people to write to them urging them to stand down. He said many candidates subsequently received thousands of messages.

“I think generally the tone of politics has deteriorated hugely, but I think our people have been subjected, certainly online, to something quite extraordinary,” he told the Guardian. “Because there has been a mass campaign organised to try and get our candidates to withdraw from standing in the election.

“If it was South America we’d all be saying something terrible was going on and call in election observers, but it’s happening here. I cannot believe that is right.”

“[Independent Group for Change MP] Anna Soubry gets a few nasty words from some lout outside parliament and everybody is up in arms,” said Farage. “That is nothing compared to what hundreds of ordinary decent people who have put themselves forward because they believe in something have suffered over the course of the last eight weeks.”

Andy Stewart, the Brexit party candidate in Doncaster North, who is mixed race, broke down when speaking to the audience in the town on Wednesday. “I’ve seen racism,” he said. “I’ve seen people banging on the door and threatening my family, but it was never like this. It does upset me because people shouldn’t be doing that at all.”

Farage said on Wednesday he expected the Conservatives to win a majority, but that British politics would be in crisis again by May because of the government’s inability to secure a trade deal by the end of next year.

Asked about the revelation earlier this week that he had been interviewed multiple times by a far-right, antisemitic American pastor between 2011 and 2016, Farage said: “I can’t even remember. Who is he?” Told that he had been interviewed at least six times, he said: “Possibly. I was doing, at one time, more than 25 interviews a day, year after year after year.”

He said that if he’d known he was antisemitic he wouldn’t have done the interview. “I obviously went on because the press officer said it was a good idea,” he added.