The new adviser on UK ministers’ interests has said he will resign if his advice is ignored, as he promised a long-delayed report that could lift the lid on whether Boris Johnson broke the rules on declaring political donations will be published by the end of May. Christopher Geidt was appointed two weeks ago to a government post that has attracted wide attention after his predecessor, Sir Alex Allan, quit in November 2020 when the prime minister overrode his finding that the home secretary, Priti Patel, bullied Home Office staff. The post has remained vacant for months, prompting speculation that Johnson was avoiding appointing a new adviser because of questions about whether he failed to declare a substantial donation he had received to help fund works reported to have cost up to £200,000 at the No 11 Downing Street flat he occupies with his fiancee, Carrie Symonds, and their son, Wilfred. After the Electoral Commission launched a formal investigation into the Conservatives and said there were “reasonable grounds” to suspect multiple offences may have been committed, Johnson announced Lord Geidt’s appointment. He was tasked with immediately conducting a review of the flat refurbishment funding and publishing the register of ministers’ interests, meant to have been released last December. Geidt said it was “unfortunate” the register had not been published in five months but, under interrogation from MPs on the public administration and constitutional affairs select committee, gave the first timeframe for its release since he was appointed. “I am absolutely determined to ensure that a full list is published as quickly as possible; I’m determined it should be published by the end of this month,” he said. “To do that, I wish to propose that all cabinet ministers’ interests should be properly resubmitted.” Geidt added that “public confidence demands that this be published without further delay” but dismissed concerns he would have trouble investigating Johnson while also advising him. He said a new “terms of reference” for his role had been drawn up that would let him “publish, in a timely manner” advice he gave to Johnson so the public would be able to see he was holding ministers to account. “Given the certainty of that daylight, I can anticipate no difficulties at all in dispassionately, impartially representing that advice to the prime minister,” Geidt said. But he did concede to the Labour MP Lloyd Russell-Moyle, who sits on the committee: “I agree that you are clearly making an observation that sunlight doesn’t appear to shine into every corner of these arrangements – and I absolutely accept what you say.” He noted that his predecessor took the “nuclear option” of resigning, and that while he hoped it would not come to that, “the power is there as a last resort” if needed. Johnson has denied he broke the rules that require all ministers to declare their financial interests, but has not ruled out the suggestion he received a loan to help foot the cost of renovations to the Downing Street flat. Separately, it was announced this week that the prime minister was being investigated by the parliamentary commissioner for standards over potential breaches of the MPs’ code of conduct, amid questions about how a holiday in Mustique at the end of 2019 was funded.