Sue Gray is refusing to cooperate with a government inquiry into her departure from Whitehall amid concerns that the investigation is politically motivated and not based on any official process. Simon Case, the head of the civil service, faced fresh questions over his handling of the controversy after ministers failed to publish the outcome of the inquiry despite widespread briefing that it would find she had broken the civil service code. Gray, who led the investigation into Partygate, took the government by surprise when it emerged she had been offered the role of Keir Starmer’s chief of staff to help Labour prepare for power. It led to the inquiry into her departure from her previous job. In a written statement on Tuesday, the Cabinet Office minister, Oliver Dowden, said Gray had chosen not to engage with the investigation, so the findings would remain confidential. “In order to maintain confidentiality towards an individual former employee, I am unable at this stage to provide further information relating to the departure of Ms Gray whilst we consider next steps,” he said. The potentially explosive report is now not expected to be published until at least after the government’s appointments watchdog decides whether to delay Gray’s start date as Starmer’s chief of staff, and it may not be published at all. Whitehall insiders said the Cabinet Office’s decision not to release the report followed 24 hours of intense negotiations over timings between Case and Tory ministers. It is understood Case initially wanted it to be published and then changed his mind. They claimed Case, who has faced criticism for his involvement in a series of crises including the Partygate scandal and Richard Sharp’s resignation as BBC chair, had “over-reached” by initially allowing plans for the publication of the findings to go ahead. The Guardian reported last week that the cabinet secretary had pushed for the Advisory Committee on Business Appointments (Acoba) to delay Gray starting her new job until after the general election next year after the pair had clashed. Several former and current permanent secretaries have privately expressed the view that Case should not stay in his job, after presiding over too many controversies and failing to stand up for the interests of the civil service. One Whitehall expert said Case needed to show leadership at a time when the civil service was facing a time of great difficulty with “workforce management, morale and relations with ministers”. The Cabinet Office report, which ministers are understood to have wanted to be made public, is said to have found that she breached the rules by holding talks with Labour about the new role without informing civil service bosses in advance. Sources suggested that despite originally backing publication, Case had become uncomfortable that a senior official could face such an investigation after they had already left the civil service, with the Cabinet Office so far unable to explain under what process the inquiry took place. Senior civil servants were also said to have been concerned about releasing such a politically charged report just days before the local elections, potentially in breach of purdah rules, and the wider implications of publicly discussing the confidential details of a former employee. Allies of Gray said the investigation, which they claim was politically motivated as she had not worked in a sensitive role for five years, was designed to put pressure on Acoba to delay her start date. While the report on Gray’s departure is separate from the body’s deliberations, it was due to be submitted as evidence. Acoba can suggest cooling-off periods of between three months and two years for senior ex-ministers or civil servants who want to take up new jobs, to minimise concerns over conflicts of interest. Whitehall sources believe the outcome of the internal investigation was intended to influence Acoba over whether there had been a perceived conflict of interest, as opposed to an actual one. The Cabinet Office denied there was any attempt to influence the appointments body. Dave Penman, the general secretary of the FDA, the senior civil servants’ union, told Times Radio: “Sue has got a right not to take part in an investigation that is being conducted under rather less clear processes. She can speak for herself or not. “She has chosen not to make any public comment because really what she is concentrating on is Acoba. She resigned as a civil servant, it doesn’t surprise me that she wouldn’t take part in a process when she is going through Acoba.” He said the Cabinet Office statement was “a bit of a damp squib” because of political briefing to the press that it would find Gray had broken the civil service code “whether to influence Acoba or to make mischief”, adding that the watchdog’s decision should be based on evidence rather than a “political game”. After its own process is completed, Acoba will share its recommendation with Rishi Sunak, who will make a final ruling, but the prime minister does not have the power to block an appointment. He is likely to take advice from Case at this stage. Downing Street is said to be keen to put Starmer, who has made a virtue of sticking to the rules, in the awkward position of having to decide whether to ignore the watchdog’s advice. The Labour leader said he was confident that Gray had not broken any rules. On Tuesday night Tony Blair’s former chief of staff described the government’s update on its inquiry as a “political stunt”. Jonathan Powell, who left the diplomatic service to work for the former prime minister, told BBC Two’s Newsnight: “We were briefed all day yesterday and today it was going to be full of these sins committed by Sue Gray and there’s been absolutely nothing in it at all. “And I’m not surprised she didn’t cooperate with it, it’s not appropriate at all. What she should be cooperating with, and she is, is Acoba, the correct body to apply to in these cases.”