Robert Mueller, US Special Counsel, is seeking more information about Nigel Farage for his investigation into Russian interference in US politics, according to an exclusive report by the Guardian.

According to the Guardian, Jerome Corsi, a conservative author, said prosecutors working for Mueller questioned him about Farage, the key campaigner behind Britain’s vote to leave the European Union, two weeks ago in Washington.

Corsi said investigators for the special counsel also pressed him for information on Ted Malloch, a London-based American academic with ties to Farage, who informally advised Donald Trump and was interviewed by FBI agents earlier this year.

“They asked about both Nigel and Ted Malloch, I can affirm that they did,” Corsi told the Guardian on November 13. “But I’m really not going into detail because I respect the special counsel and the legal process.”

Mueller’s interest in Farage comes amid questions in the UK about whether Russia attempted to influence the June 2016 vote to leave the European Union, and Brexit’s most vocal political supporters.

A spokesman for Farage said of Corsi’s allegations: “This is ill-informed, intentionally malicious gossip and wholly untrue.”

The Guardian also reported that Andy Wigmore, a spokesman for the pro-Brexit Leave campaign, said Farage had not been contacted by Mueller’s team.

Also, Malloch’s publisher, Nick Magliato, said Malloch’s lawyer instructed the academic, who is in London, not to comment.

Corsi and several other conservative operatives in the US have been under investigation by Mueller for months in relation to the theft of Democratic party emails in 2016 by Russian hackers, which disrupted Hillary Clinton’s presidential campaign.

Farage has denied any involvement with Russia. However, he forged close ties with the Trump campaign and White House through his close friendship and association with Steve Bannon, the former Breitbart editor and White House strategist.

The Guardian first reported in June last year that Farage was a “person of interest” in the Russia investigation.

Asked if the questions on Farage related to Trump’s 2016 election campaign or that year’s referendum on the UK leaving the EU, Corsi said on November 12: “Predominantly US politics, but of course Brexit was in the background.”

Corsi has said that Mueller’s questioning focused on the theft of emails from Clinton’s campaign and the Democratic National Committee, which were published by WikiLeaks. US intelligence agencies concluded the emails were stolen in a Russian intelligence operation.

He said: “The issue they went to over and over and over again was: who was my source with Assange?”

According to the Guardian, Corsi conceded on November 13 that he had sent emails to associates boasting of inside information from WikiLeaks about the plan to publish the emails but insisted that he was merely trying to boost his reputation and in fact only knew information that was already public.