A billionaire US hedge fund executive and major donor to US Republican candidates invested £1m in a British company owned by a Conservative peer who was close at the time to the then prime minister, Boris Johnson. Kenneth Griffin, the founder of Citadel, one of the largest hedge funds in the world, made the personal investment in 2020 in a company set up by Lord Howard of Rising, a Conservative peer whose Westminster mansion served as Johnson’s leadership campaign “nerve centre” a year earlier. Lynton Crosby, the Australian strategist who is considered the political mastermind behind electoral campaigns for Johnson, David Cameron and Theresa May, joined the company, Dalbini Limited, as a director three months after the investment by Griffin, according to Companies House records. Sometimes referred to in press reports as the “Wizard of Oz” due to his successful election campaigns, Crosby was brought back as an adviser to the Tory party to help when Johnson’s premiership was in crisis amid the Partygate scandal, which revealed that multiple parties had been held in and around 10 Downing Street during the height of the Covid pandemic. Crosby came under scrutiny during this period over lobbying by his CT Group on behalf of clients. He denied any potential conflict of interests. Company accounts suggest that about £560,000 of funds Griffin and Howard invested had been used by March 2022. The records do not provide more information about how the money was spent. The hedge fund executive made the investment in Dalbini a year after he expanded his presence in London by buying a Grade II*-listed Georgian mansion in the heart of Westminster for £95m. A spokesperson for Griffin, one of the world’s richest men, said he had made the personal investment in Dalbini as part of a plan to establish “one or more media ventures” in the UK “that would compete with the Guardian and other news organisations”. Crosby, speaking on behalf of Dalbini, said in a statement that the company was now dormant and that the investment opportunities it had examined were “entirely commercial in nature”. He added that Dalbini “had no connection to politics whatsoever”. The investment raises questions, however, about why Griffin – who has an estimated net worth of $35bn – would personally invest in a company established by a British peer with close links to key political figures. Griffin was the third largest donor in the US midterm election last year, having donated about $73m to Republican candidates. He has also donated millions of dollars to the Florida governor, Ron DeSantis, who is running for the Republican nomination for president. It is not yet clear who Griffin – who does not support Donald Trump – will back in the upcoming contest for the Republican nomination. The billionaire made the £1m investment in Dalbini via a private company, Media Holdings LLC. A person close to him said it was a “purely personal” investment and unrelated to his hedge fund company Citadel. The spokesperson described Howard as someone who had been a personal friend of the hedge fund executive for many years. In a seeming breach of parliamentary rules, Howard, a Eurosceptic member of an English aristocratic family, had not declared full details about his involvement in Dalbini in the House of Lords register of interests until he was contacted by the Guardian. The rules require members of the House of Lords to disclose details about the nature of a company’s business when not apparent from its name. However, while Dalbini was active, Howard failed to disclose those details. When initially contacted, Howard described Dalbini’s business activities as “confidential”. About a month later his office amended his disclosure. “Once you raised the lack of explanation of Dalbini’s activities in Lord Howard’s register of interests in the House of Lords, the register has been updated. He appreciates you drawing this to his attention,” Howard’s secretary wrote in an email. She added: “Dalbini researched possible opportunities but made no investments.”