Mark Fullbrook, the new Downing Street chief of staff, has been interviewed by the FBI as a witness about work he did for a banker accused of bribery, it emerged on Sunday. Fullbrook was working as a political consultant when he provided research in 2020 for Julio Herrera Velutini, a Venezuelan-Italian banker accused of bribing the governor of Puerto Rico around the same time. A senior organiser in Conservative party politics for decades, who was appointed chief of staff at No 10 after running Liz Truss’s campaign for the Tory leadership, Fullbrook has said that he did not break the law and that he was not aware that his then client may have had corrupt motives for hiring him as a consultant. According to the US indictment, Herrera Velutini offered to contribute to Wanda Vázquez Garced’s campaign for re-election as governor of Puerto Rico in return for Vázquez Garced sacking the island’s financial regulator, who was investigating Herrera Velutini’s bank. It is alleged that Herrera Velutini offered support worth $300,000. The launch of the proceedings in the US provoked controversy in the UK because Britannia Financial Services, a company set up and largely owned by Herrera Velutini, has given more than £500,000 to the Conservative party since 2019. Labour said that, in the light of the allegtions against the banker, the Tories should give the money back. Herrera Velutini denies wrongdoing and is contesting the charges against him, which carry a total maximum penalty of 20 years in jail. Fullbrook is involved because at the time he was working for CT, a political consultancy founded by Sir Lynton Crosby, who has run general election campaigns for several Tory leaders. Herrera Velutini was paying CT for consultancy services that might have helped Vazquez Garced in her re-election bid. According to a report in the Sunday Times, Fullbrook was the lead consultant on the project and flew to Puerto Rico in February 2020, six months ahead of the election. The firm produced opinion research relevant to the campaign. Vázquez Garced did sack the financial regulator in February 2020, but went on to lose her re-election campaign anyway in August that year. According to the Department of Justice indictment, Herrera Velutini then tried to bribe her successor, by offering funding in return for a favourable audit of his bank. According to the Sunday Times, the FBI approached the National Crime Agency and the Metropolitan police in April this year to secure Fullbrook’s attendance at a formal interview. Fullbrook is being treated as a witness in the case. A spokesperson for Fullbrook said he obeyed the law in all countries where he worked and that he was confident he had done so in this case, too. The spokesperson went on: “Indeed, Mark Fullbrook is a witness in this matter and has fully, completely and voluntarily engaged with the US authorities in this matter, as he would always do in any circumstance in which his assistance is sought by authorities.” According to the spokesperson, Fullbrook did not know of Herrera Velutini’s alleged intention to bribe the governor when CT was working for him and Fullbrook only learned about this allegation in April 2022. The spokesperson also said that, while Fullbrook did meet Vazquez Garced, he never produced any work for her. The opinion research carried out by the company was provided to Herrera Velutini, the spokesperson said. As the US Department of Justice disclosed in August, two people – a banker and a political consultant from Puerto Rico – have already pleaded guilty to consipiring with Herrera Velutini to bribe a public official. At the time the US attorney for Puerto Rico, William Stephen Muldrow, said: “The criminal actions of the defendants in this case strike a blow to the heart of our democracy and further erode the confidence of our citizens in their institutions of governance.” Downing Street declined to comment on the story.