The businessman and Reform UK backer Arron Banks commissioned a private intelligence firm to dig into the Conservative party chair, in addition to having paid for an investigation into a prominent journalist.

Banks, a former Reform UK candidate and leave campaign donor, appeared to confirm on Sunday that he was behind an investigation into Kevin Hollinrake.

The use of private investigators to look into Hollinrake was first reported by the Mail on Sunday, which said Banks had used Precision Risk and Intelligence, a firm he previously owned.

As party chair, Hollinrake has led the Conservatives’ response to revelations about Nigel Farage’s finances, asking questions about the £5m undeclared gift Farage received from the Thailand-based crypto billionaire Christopher Harborne before the last election.

Hollinrake addressed Banks on social media on Sunday, saying: “When you can’t answer the questions, investigate the people asking them. After we called for scrutiny of Reform UK’s finances, a close associate of Nigel Farage reportedly hired private investigators to dig into me (and journalists covering the same story).”

In a reply on X, Banks said: “I’ve always come across people in this world who like to give it but can’t receive it.”

Pressed on whether Reform knew about the surveillance, Banks suggested he had acted alone, saying: “I row my own boat.” Banks has been approached by the Guardian for comment.

The developments come after it emerged previously in the New Statesman that Banks had commissioned Precision Risk to investigate Gabriel Pogrund, the investigations editor of the Sunday Times.

The revelation led to fears that other journalists examining the funding of Reform and Farage, including those at the Guardian, could have been targeted.

When asked previously whether he had commissioned investigators to surveil reporters at the Guardian, Banks said he was “not really interested in the Guardian” but declined to comment further.

The News Media Association (NMA), which represents regional and national media, raised concerns and described it as an “attack on our democracy”.

The Guardian, along with the Sunday Times, has broken a series of stories in recent months revealing how cash has been given to Reform and Farage personally from donors and wealthy benefactors.

Theo Bamber, the chief executive of the NMA, said aggressive attempts to deter journalistic inquiry were at risk of becoming normalised.

He said: “Using private investigators to try to deter journalists from making legitimate inquiries about public figures is an attack on our democracy. Sadly, intimidation and abuse of local and national journalists is increasingly used as a weapon to limit scrutiny and deflect attention away from matters of public interest. This must not become normalised.

“Ministers must wake up to this threat to our democracy and do much more to protect the independent journalism which underpins our democratic way of life.”

Banks previously told the New Statesman: “We believe the Sunday Times used hacked information and that was an area of interest. We do have an investigative arm that’s got advanced capabilities.”

The Sunday Times has rejected Banks’s suggestion. Banks, when asked directly by the New Statesman whether he had paid investigators to look into Pogrund, responded: “When you live by the sword, you die by the sword.”

The Sunday Times published a new investigation this weekend into links between Reform funders and Tether.bet, a website accused of illegally offering gambling to UK punters, which closed this week.

The newspaper said the convicted fraudster George Cottrell was a high-profile customer of the website, and Harborne owned a company, IFX, that processed payments on behalf of another company that took deposits and returned winnings.

Cottrell’s lawyers told the newspaper his relationship with Tether.bet “has been limited to that of a customer, in addition to which he knows and is friends with the owner”.

When contacted by the Guardian, Cottrell’s lawyers said he was one of the world’s best-known professional gamblers. “It is therefore hardly surprising that [others] may seek to associate themselves with him in an attempt to lend credibility to their businesses or generate publicity. Mr Cottrell has never invested in, owned or operated any betting company or casino. He has never solicited clients for any betting company or casino. Any suggestion that he was involved in unlawful gambling activity is wholly false.”

Harborne and IFX’s representatives told the Sunday Times he had never had any role in the running and operations of IFX and that it “operates in accordance with applicable regulations and legislation across the markets it supports”.

A Labour spokesperson said in response: “These reports raise yet more questions about the people bankrolling Reform and Nigel Farage … Farage cannot run from the truth for ever. The mountain of unanswered questions around his finances and judgment is only getting bigger. He needs stop the excuses, come clean with the public.”