Nigel Farage, the leader of Britain’s right-wing Brexit Party, has been drenched by a milkshake thrown by a protester in the northern English city of Newcastle.

Farage, who has come under fire in recent days for refusing to release a political manifesto for his party ahead of European elections, was heard berating his security team moments after being hit with what is understood to have been a banana and salted caramel-flavoured shake.

“This is a failure,” the Newcastle Chronicle reported him as saying. “How did that happen?”

The former UKIP leader had been campaigning in the town for 20 minutes when the attack happened. A 32-year-old man is in custody, police confirmed.

Paul Crowther says he threw the milkshake over Farage on Monday. “It’s a right of protest against people like him,” he told the Press Association. “The bile and the racism he spouts out in this country is far more damaging than a bit of milkshake to his front.”

Farage has previously threatened to “don khaki, pick up a rifle and head for the front lines” if Brexit were not delivered, but, after being whisked away following the milkshake incident, said it was his opponents who had become “radicalised”.

“Sadly some remainers have become radicalised, to the extent that normal campaigning is becoming impossible,” he tweeted.

Farage is only one of several right-wing populist figures to have been hit with a milkshake in recent weeks.

Tommy Robinson, real name Stephen Yaxley-Lennon, the former leader of the English Defence League now standing for the European Parliament in north-west England, has been doused twice. Carl Benjamin, a UKIP European Parliament candidate for south-west England who has infamously refused to apologise for tweeting “I wouldn’t even rape you” at the Labour MP Jess Phillips, has been hit four times so far on the campaign trail, with the latest drenching just moments after Farage’s, hundreds of miles away in the town of Salisbury.

Right-wing figures are warning that this trend of “milkshaking” is a stepping stone to more worrying political violence, with some even comparing the lobbing of food products to the fatal shooting of Labour MP Jo Cox during the EU membership referendum campaign.

On Saturday, when Farage was visiting Scotland, McDonald’s in Edinburgh said it would not be serving milkshakes after a police request. Burger King tweeted that it would be selling milkshakes all weekend, and encouraged its customers to “have fun”.

Funding questioned

Farage’s Brexit Party has had the sources of its funding questioned. Former Prime Minister Gordon Brown told a Labour campaign rally on Monday that the Brexit Party was not a political party at all, but rather a private company. “It doesn’t have members, it has shareholders,” he said.

The UK Election Commission announced on Monday that it would be investigating the Brexit Party. “We are attending the Brexit Party’s office tomorrow to conduct a review of the systems it has in place to receive funds, including donations of over £500 that have to be from the UK only,” it said in a statement.

Brown had earlier suggested the anonymity of online donations raised serious questions over the potential for foreign funding. “He’s not going to be remembered as he wants, as the man of the people,” said Brown. “He’s going to be remembered as the man of the PayPal.”

Farage is also facing an investigation by EU authorities for failing to declare more than half-a-million dollars in “gifts” – a car with driver, rent for a multimillion-dollar Chelsea home, and tours of the United States with right-wing politicians – allegedly received from insurance salesman Arron Banks.

Farage has denied any wrongdoing, saying any gifts received had nothing to do with his political work. “It’s a purely private matter, non-political in absolutely every way,” he told Channel 4 news.

Banks was the force behind Leave.EU, one of the main anti-Brexit campaign groups, and is currently under investigation by the UK’s National Crime Agency over his bankrolling of populist political anti-Europe groups and politicians.

“Arron Banks is believed to have donated £8.4 million [$10.7m] to the Leave campaign, the largest political donation in British politics, but it is unclear from where he obtained that amount of money,” read a November 2018 report from the Digital, Culture, Media and Sport committee of the UK’s House of Commons.

“He failed to satisfy us that his own donations had, in fact, come from sources within the UK. At the same time, we have evidence of Mr Banks’ discussions with Russian Embassy contacts, including the Russian Ambassador, over potential gold and diamond deals, and the passing of confidential information by Mr Banks.”

Banks also denies any wrongdoing.