A Cabinet Office inquiry into allegations of bullying by Priti Patel has found evidence that she broke the ministerial code, informed sources have told the Guardian. Boris Johnson, the sole arbiter of the rules, is expected to release a decision on the inquiry within weeks but it is not likely to demand the home secretary’s resignation. Sources familiar with the inquiry said it had found evidence that civil servants were treated poorly by Patel, as well as compelling evidence of bullying. Pressure on the prime minister to sack Patel is growing as a result of claims of bullying and harassment from civil servants in three separate government departments. Speculation over the inquiry has prompted condemnation of the Cabinet Office inquiry process, which is conducted in secret and offers no recourse for complainants. Johnson has already been criticised for compromising the process by insisting before the inquiry had ended that he would continue to support Patel. Patel has denied allegations of bullying. Allies have described her as a “demanding” boss but not a bully. Allegations against the MP for Witham emerged in March after the resignation of Philip Rutnam, the former Home Office permanent secretary, over what he described as a “vicious and orchestrated campaign” against him for challenging the alleged mistreatment of civil servants. According to reports, a senior Home Office official collapsed after a fractious meeting with Patel, who is understood to have successfully asked for another senior official in the department to be moved from their job. It also emerged that an official in the Department for Work and Pensions (DWP) had received a £25,000 payout after she alleged that she had been bullied in 2015 by Patel, who was employment minister at the time. The DWP did not admit liability and the case did not come before a tribunal. Officials in Patel’s private office at the Department for International Development allegedly accused her of humiliating civil servants in front of others while a minister in 2017. Patel is also facing the possibility of being questioned at a 10-day employment tribunal hearing next September after lawyers for Rutnam pushed forward with a claim for constructive dismissal. The Cabinet Office inquiry was launched in March by Michael Gove and conducted by Helen MacNamara, the civil service’s head of ethics. The prime minister has been advised by Alex Allan, Whitehall’s independent adviser on ministerial standards. It was completed at the start of the summer and forwarded to No 10. It is understood that some in government will claim that Patel’s behaviour towards staff had been “unintentional”, because she was unaware of the effects of her actions. Rutnam’s tribunal claim alleges that bullying behaviour aimed at him, through anonymous briefings to the media, intensified after he had raised staff concerns with Patel about her behaviour. A sleaze watchdog criticised Johnson last week for failing to rule on the inquiry’s findings. Jonathan Evans, the former head of MI5 and now adviser on standards in public life, told the Times: “When you have got these allegations that have not really been put to bed then it’s easy to say they’ve just been brushed over and I don’t think that’s ideal for public trust and public standards. “The Priti Patel case would be an example. The Cabinet Office has done some form of investigation. It has not been published so it is very difficult to know whether there was something here or whether there wasn’t.” Dave Penman, the head of the FDA union which represents senior civil servants, said that if any substance had been found in any of the allegations against Patel, the prime minister should conclude that the code had been breached. “Having pledged his support for the home secretary when the investigation began, and now sat on the report since the summer, he has already undermined confidence in this being a fair and impartial process. “Boris Johnson now needs to make the decision to publish the report and commit to introducing a new, fully independent and transparent complaints system. This is the only way to restore any kind of faith in the process and prevent this kind of drawn out speculation in the future, which is unfair to both victims and those accused,” he said. The ministerial code says “harassing, bullying or other inappropriate or discriminating behaviour” will not be tolerated. Ministers are “personally responsible” for how they act, it says, and they can stay in office “for so long as they retain the confidence of the prime minister”. A government spokesman said: “The process is ongoing and the prime minister will make any decision on the matter public once the process has concluded.”