A Cabinet Office investigation into several allegations about Ms Patel's behaviour was launched in March.

Shadow home secretary Nick Thomas-Symonds wrote to Cabinet Office Minister Michael Gove on Saturday, saying that the delay in publishing the findings was "unacceptable".

Ms Patel denies all the allegations.

The Cabinet Office said the process was "ongoing" and it would respond to the letter "in due course".

The MP for Witham faces accusations she mistreated staff in her current role as home secretary.

Prime Minister Boris Johnson - who has said he is "sticking by" Ms Patel - asked the Cabinet Office to establish the facts following the claims levelled against her.

The report is understood to have been completed.

In the letter to Mr Gove, Mr Thomas-Symonds and shadow Cabinet Office minister Rachel Reeves said the delay "creates the clear sense that the government is acting in the interests of a Conservative Party elite, rather than the national interest".

They added: "We have been asking frontline public servants to make extraordinary sacrifices throughout this pandemic and it is only right that they have full faith in those in government who make demands of them.

"This report must now be published immediately for it to be properly considered before recess begins, and we look forward to your confirmation of this."

The investigation was launched by Cabinet Secretary Sir Mark Sedwill - who has since announced his resignation following reports of tensions between him and senior members of the PM's team in Downing Street.

Senior Cabinet Office official Helen McNamara and senior civil servant Alexander Allan are compiling the report.

The letter follows a report in The Times of a "stand-off" between senior officials and political aides over the publication of the report.

The paper said Ms MacNamara was refusing to exonerate Ms Patel from some of the allegations of bullying, despite the PM's aides supposedly wanting the inquiry to find there was no conclusive evidence of bullying.

Mr Thomas-Symonds said in the letter: "It has been over four months since the government promised a report into whether the home secretary broke the Ministerial Code.

"There are now allegations of deeply inappropriate political interference in the publication of the report, both in terms of content and timing. The delay in producing it is totally unacceptable."

A Cabinet Office spokeswoman said: "The prime minister asked the Cabinet Office to establish the facts of the case, in line with the Ministerial Code.

"That process is ongoing and we will respond to the letter in due course."

In February, Sir Philip Rutnam resigned as the Home Office's permanent secretary, saying there had been a "vicious and orchestrated" campaign against him in the department. The inquiry is separate to the employment tribunal claim lodged by Sir Philip.

Ms Patel's allies said the home secretary was a "demanding" boss but not a bully.