The House of Commons standards watchdog has hinted Gavin Williamson could be investigated for bringing parliament into disrepute over bullying allegations, as she raised concerns about public anger and despair about the behaviour of some MPs. Kathryn Stone, the parliamentary commissioner for standards, said it was deeply frustrating to the public that she did not have power to investigate 1,500 complaints about Boris Johnson’s Partygate scandal or Matt Hancock’s decision to prioritise a “buffet of animal genitalia” on ITV’s I’m a Celebrity over his job in parliament. She also called on Rishi Sunak to appoint an ethics adviser following the resignation of Christopher Geidt earlier this year, because the gap in the system meant alleged breaches of the ministerial code were not being investigated. “Somebody needs to make a decision, and make a decision soon, about what happens to ministers who breach or are alleged to have breached the ministerial code,” she said. “I’m not the only voice that has said publicly the prime minister really needs to make a decision about the appointment of a replacement for Lord Geidt.” She added: “It can’t be easy to sit as a backbench member of parliament and know that you are subject to more careful scrutiny about gifts, hospitality, financial interests than someone who is a minister or secretary of state.” But asked whether she could investigate claims that Williamson, as chief whip, told an MP bailed out of financial difficulty that “I now own him”, Stone said she could not comment because of the risk of potentially prejudicing an investigation. “I have to consider very carefully any live case and I don’t want to prejudice or undermine any investigation into a live case,” she said. Labour has written to Nadhim Zahawi, the Conservative party chair, asking for urgent answers about whether the alleged financial bailout for an MP was declared as a gift in the register of interests, and whether Williamson consulted the Conservative party about the move. Giving evidence to parliament’s standards committee, Stone said she had received dozens of complaints about the former health secretary Hancock swapping Westminster for the Australian jungle to appear on I’m a Celebrity, but it could not be investigated. “It raises really important questions about members’ proper activities while they’re supposed to be fulfilling their parliamentary duties and representing their constituents,” she said. “One member of the public contrasted the dignity of veterans on Remembrance Sunday with a former secretary of state and they said this individual was waiting for a buffet of animal genitalia and they wondered what had happened to the dignity of public office.” She said the Partygate fines received by Johnson and Sunak had resulted in almost 1,500 complaints to her office, while she also received about 800 over “a newly appointed education minister making an offensive gesture” – a reference to Andrea Jenkyns raising her middle finger at crowds outside Downing Street before Johnson’s resignation statement. Stone told the committee she believed the public had gone from “anger to despair” over the conduct of MPs in recent years and she had faced “death threats” as part of her job. “I have been subject to death threats, I have been subject to very serious security threats, received incredibly abusive correspondence. I think those of us who work in public life understand very well what those pressures are.” Several MPs on the committee challenged the idea that MPs should be subject to public anger about their behaviour, saying that only 3% have been found to have done anything wrong. One Conservative backbencher, Sir Charles Walker, said he wished he “had someone to write to about the anger, desperation and despair I have about the conduct of a minority of my constituents”, as he highlighted the abuse many MPs have faced.