Staff have reportedly accused the home secretary of belittling officials, taking an angry and aggressive tone in meetings and making unreasonable demands of civil servants.
Ms Patel was said to have demanded the removal of her permanent secretary, Sir Philip Rutnam, after he reported concerns over her behaviour to the Cabinet Office, according to The Times.
But business minister Nadhim Zahawi, who has known Ms Patel for 25 years, denied she was a bully, saying she was “utterly professional” and a “brilliant, collegiate team player”.
It comes after Ms Patel was branded "clueless" for suggesting that staffing shortages caused by her tough new immigration plans could be filled by 8.5 million “economically inactive” Britons - most of whom are students, retired or living with long-term illnesses.
Tensions appeared to come to a head last week when an official collapsed after a tense meeting with Ms Patel. He had been working through the night to overturn a High Court ruling barring the deportation of foreign nationals to Jamaica.
The official fell ill later during another meeting and was taken to hospital, where he was found to have a sodium deficiency.
A Home Office source told the newspaper she was an "extraordinary person to work for", adding: “No one can see how this is going to be resolved. It is going to blow up sooner or later.”
Another source said: “Sir Philip and [Ms Patel] have fundamental disagreements about the rule of law.
“He’s committed and she isn’t. She’s belittled him and caused consternation, and she frequently encourages behaviour outside the rule of law.”
A Home Office spokesperson said: “We have not received any formal complaints and we take the welfare of our staff extremely seriously.”
Mr Zahawi told LBC he had not seen the details of the allegation but denied that Ms Patel was a bully.
The Tory MP said: “I don’t think she is. I’ve known Priti for 25 years. She’s utterly professional, works night and day to deliver for the country and her constituents and is absolutely focused on making sure...the people voted for us to take back control of our borders.”
Pressed on whether she was a bully, he said: “No I don’t think she is at all.
“I’ve worked with Priti in the past in several campaigns. I’ve known her literally for 25 years. She is a brilliant, collegiate team player.”
Allies of the home secretary also rejected the claims bullying, saying Ms Patel was a demanding boss but never unreasonable.
“The Home Office is dysfunctional and the current permanent secretary had presided over a sacking of a home secretary and accidental deportations,” they said.
“If this were any other environment Philip Rutnam would not only be sacked he’d be denied a pension. The lack of accountability in the civil service is deeply troubling and the prime minister will not accept this in the long term.”