HOME Secretary Priti Patel “unintentionally” broke the Cabinet rules, a Whitehall bullying probe has concluded.
But Boris Johnson is unlikely to sack his close ally after her department was also blasted for poor performance.
A row exploded in February after top civil servant at the Home Office Sir Philip Rutnam quit, saying Ms Patel mistreated staff by swearing and shouting - claims she has always denied.
But the formal probe into the affair has concluded that her frustration with the poor leadership from officials in her department was justified, and no concerns were raised with her about bad behaviour.
The investigation is likely to warn civil servants working at the Home Office must also “reflect” on their behaviour after ignoring Ms Patel's orders.
But the Sun understands it will also flag up strict rules for ministers that state that they must treat staff with “consideration and respect" at all times.
The Prime Minister will tomorrow rule on the formal investigation conducted by top Whitehall sleaze-buster Sir Alex Allan who advises Mr Johnson on bad behaviour.
But insiders suggested Ms Patel was unlikely to face the chop due to the widespread criticism of all involved in a draft of the report.
A well placed source said Mr Johnson was "absolutely standing by Priti".
Insiders said the probe has found Ms Patel was unaware of any concerns due to a lack of leadership from senior mandarins - meaning any complaints were not able to be addressed at the time.
It is understood that the report finds there has been a dramatic improvement in relations between the Home Secretary and her officials in recent months after a change of guard in the department.
A summary of the findings is due to be released tomorrow, but Labour have demanded the whole document be published "immediately".
Shadow Home Secretary Nick Thomas Symonds warned :“These revelations could not be more serious."
He added: “This has all the hallmarks of a cover up from the Prime Minister and raises fundamental questions about his judgement.”
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But former Tory leaders Sir Iain Duncan Smith leapt to Ms Patel’s defence, saying she "is strong willed and determined to get the job done."
The grandee added: “There is a history of poor civil service leadership at the Home Office and the report is critical of that.
"She is no bully but a good minister.”
And Conservative MP Dr Kieran Mullan said: "Having worked closely with Priti Patel I never saw any bullying behaviour, just someone determined."
He added: "Nobody is perfect and I'm sure she would be gracious about doing things differently, but being told 'computer says no' by officials sometimes takes grit to get through."