Sue Gray, the permanent secretary investigating “partygate”, has a task that grows in political significance almost every day. She was for many years the head of propriety and ethics at the Cabinet Office. That role essentially does all the tricky political stuff, from investigating ministers’ conduct to vetting political memoirs. I’ve known Sue for more than a decade and she is formidable, but none of that should matter. That alone is not good enough for the public to blindly trust that she will be allowed to deliver the unvarnished truth, when the stakes are as high as they can be, and everyone knows her report could determine the fate of the prime minister. The civil service is often called upon to deliver the most uncomfortable messages to ministers. Indeed, it is deliberately set up to do so. Civil servants cannot be hired or fired by ministers. They are permanent. They have a duty of integrity, honesty, objectivity and impartiality under the civil service code. This means that they must act in a way that retains the confidence not only of this government, but also a future one. Again, blind trust is not required from the public. We know civil servants seek to do the right thing. Following the resignation of Sir Philip Rutnam, the then permanent secretary at the Home Office, live on BBC News, Michael Gove, then Cabinet Office minister, went to parliament and announced an investigation into the allegations that the home secretary had bullied civil servants. Two days later, pressed at prime minister’s questions, Boris Johnson delivered his infamous “I’ll stick with Prit” line, despite knowing that he would ultimately be required by the established rules to pronounce on her guilt or innocence. Fast forward nine months and Johnson’s decision that she did not breach the ministerial code, despite the evidence that she had bullied staff – including shouting and swearing at them – resulted in the resignation of Sir Alex Allan as the independent adviser on ministers’ interests. My union, the FDA, sought to challenge Johnson’s decision by way of judicial review. As part of that process, we uncovered that two months after the investigation was launched, in May 2020, Johnson was handed a draft report. What followed is unclear but, given subsequent events, it’s a pretty safe bet that he was not entirely thrilled by its contents. By July 2020, Johnson had the final report with recommendations from Sir Alex. Clearly unhappy, he sat on the report for a further five months until its publication was essentially forced on him by leaks. Only the civil service came out of that debacle with any integrity. Against what must have been the most intense political pressure from the prime minister, civil servants stuck to the truth and the facts that they had uncovered. Sue Gray’s report will be factual, and in all likelihood uncomfortable for many in No 10. The weakness in the system, though, is not her ability to report the truth. It is in the control the prime minister has over what happens next. For any civil servant implicated in misjudgment or wrongdoing, the process is clear and disciplinary action may follow under Cabinet Office rules – but what about Johnson himself? That is the element that should truly concern the public. If the evidence suggests that the ministerial code has been breached only Johnson can sanction an investigation into ministers and, perversely, into himself. Johnson chose to retain that power despite the recommendations from the committee on standards in public life that it should go. The public can trust the civil service to deliver the facts. The bigger question is can it then trust the prime minister to do the right thing? Dave Penman is the general secretary of the FDA union