Former senior official Sue Gray is facing a “political witch-hunt”, allies believe, with the government set to conclude that she broke the civil service code, in an alleged bid to delay her appointment as Keir Starmer’s chief of staff until after the next general election. Ministers are expected to announce on Tuesday that an internal inquiry into Gray’s departure from Whitehall has concluded that she breached the code by holding talks with Labour about the new role without informing civil service officials. However, it is believed to be unprecedented for a senior official to face such an investigation after they have already left the civil service, and the Cabinet Office has so far been unable to explain under what process the inquiry took place. Gray’s supporters believe that the investigation, which they claim is politically motivated as she had not worked in a sensitive role for five years, is designed to put pressure on the government’s appointments watchdog to delay her starting the new job. They fear the Advisory Committee on Business Appointments (Acoba) could recommend that Gray, recruited to lead Labour’s transition into government, should be banned from working for the party until after the next election, expected next autumn. The official watchdog 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 potential – or perceived – conflicts of interest. Cabinet Office insiders have acknowledged their investigation into Gray’s departure, to be announced in a written ministerial statement, is separate from the Acoba deliberations. However, sources suggested they wanted a a one-year delay. Whitehall insiders said the interim findings had concluded Gray had breached the code, claiming that the move was intended to influence Acoba over whether there had been a perceived conflict of interest, rather than an actual one. Last week sources said that the head of the civil service, Simon Case, wanted to block Gray from working for Labour for as long as possible, but a minimum of one year. Case, who signed off Gray’s Acoba application, is understood to have personally clashed with her during her Partygate investigation and afterwards, when he blocked her promotion to a more senior role, effectively limiting her career prospects within the civil service. 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 also 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. Government sources have denied the move is “personal”, saying they refute the suggestion that Gray’s progress in the civil service was blocked by Case. They added that no action was taken against Case as part of the Partygate investigation so there would have been no reason for any tensions between the pair.