Rishi Sunak must ask his ethics adviser to help decide whether Dominic Raab is a serial bully or risk losing the public’s trust, a union leader has said. The prime minister alone will decide whether his deputy and justice secretary has broken the ministerial code after eight separate complaints across three ministerial departments. Under the bullying inquiry’s terms and conditions, the independent investigator Adam Tolley KC will only “establish the specific facts” surrounding the claims, which Sunak will then rule on. Dave Penman, the general secretary of the FDA union, has written to Sunak on Wednesday calling for the independent adviser on ministerial interests, Sir Laurie Magnus, to join the prime minister in examining Tolley’s findings and come to a judgment on Raab. “The role of the independent adviser in determining on those facts and advising you in relation to the allegations and the ministerial code is critical in providing confidence to civil servants and the public,” he said. “I want to make clear, we are not in any way raising a concern as to the integrity or conduct of Adam Tolley KC – quite the opposite. It is the lack of any independent input into the decision-making following his investigation that is concerning us.” Sunak is coming under growing pressure to say what he knew about the claims about Raab when he was appointed in October. Critics were concerned by Sunak’s interview with the BBC’s Chris Mason in November in which he repeatedly declined to say whether he had received informal warnings about Raab’s alleged bullying behaviour before bringing him back into the cabinet. Penman, alluding to the interview, wrote that Sunak’s lack of clarity had undermined trust in the investigation’s process. “Over the last few months you have deliberately chosen not to answer a direct question on whether you were aware of concerns over the conduct of the deputy prime minister when you appointed him. You have also repeatedly relied on the lack of a formal complaint as an evasion tactic over this issue,” he said. There had been a lack of formal complaints against Raab, Penman said, because Priti Patel kept her job as home secretary despite a formal inquiry finding evidence she had bullied her staff. “The formal complaints process was fatally undermined by the decision of the then prime minister, Boris Johnson, to ignore the findings of bullying against Priti Patel. It can therefore come as no surprise to any interested party that civil servants had no confidence in the process of raising formal complaints under the ministerial code,” Penman wrote. Magnus, a former banker and quango head, was appointed as Sunak’s ethics adviser in December after a six-month delay in filling the post. In his first major inquiry, Magnus found last month that the Conservative party chair, Nadhim Zahawi, had made a “serious breach” of the code by not telling officials he was under investigation by the tax body when he was appointed chancellor by Johnson. Zahawi was subsequently sacked. He took over in the role from Christopher Geidt, who resigned as the independent adviser on ministers’ interests under Boris Johnson in June after disagreements over the handling of the Partygate affair. In November 2020, Sir Alex Allan resigned in protest from the same job after Johnson refused to sack Patel despite the findings of the bullying investigation. Tolley, who has experience of handling whistleblower claims, was appointed by Sunak in November to investigate complaints “in confidence”. Penman’s demands come as Raab fights for his political career while facing allegations from dozens of civil servants. The deputy prime minister denies any wrongdoing. The Guardian disclosed last week that all three mandarins who worked with Raab while he was holding cabinet positions had been interviewed by Tolley. The Guardian first disclosed claims of bullying against Raab in November. Asked to respond to the substance of Penman’s letter, a No 10 spokesperson said: “The prime minister has asked for the facts to be established and these will be set out by the independent and experienced barrister carrying out this work, Adam Tolley KC.”