The party said Boris Johnson must clear up suggestions that Helen MacNamara, a senior civil servant, is refusing to clear the home secretary of all charges as Downing Street is demanding.
“There are now allegations of deeply inappropriate political interference in the publication of the report, both in terms of content and timing,” said Nick Thomas-Symonds, Labour’s shadow home secretary
“The delay in producing it is totally unacceptable,” he added – arguing it had been held up for four months.
It is six weeks since a leak appeared to suggest that the internal investigation had found no evidence that Ms Patel had mistreated civil servants, in three different departments.
But The Times has reported a stand-off between Ms MacNamara, the Cabinet Office’s head of propriety and ethics, and her political masters.
Her inquiry is understood to have heard evidence to substantiate the bullying claims made by Philip Rutnam, the Home Office permanent secretary, who sensationally quit in February.
The article suggested the inquiry report will never be published, unless the prime minister is able to say the investigation found no conclusive evidence of bullying, an outcome that Ms MacNamara is resisting.
Mr Thomas-Symonds added: “It has been over four months since the government promised a report into whether the home secretary broke the ministerial code.
“Yet again the government is acting in the interests of a Conservative Party elite, rather than the national interest. I’ve written to the minister for the cabinet office calling for the report to be published immediately.”
Dave Penman, general secretary of the FDA union representing public service managers, echoed the criticism.
“No decision or timetable for decision + No obligation on PM to publish report + No rights for any alleged victim to challenge report = Ministerial Code not fit for purpose,” he tweeted.
Downing Street declined to comment on the suggestions of political interference, or on the timing of the report’s publication – with the Commons going into its summer recess on 22 July.
Ms Patel faced a “tsunami of allegations” – all of which she denies – that she humiliated civil servants in front of others during her time as international development secretary and gave the impression that “everyone is hopeless”.
While she was the work minister, an official in her private office allegedly tried to kill herself after being bullied and later received a £25,000 payout from the government.
The latest controversy comes after Mr Johnson authorised a near-£250,000 payment to Mark Sedwill, the ousted cabinet secretary – an apparent admission that he had, in effect, been sacked.
Politicians and legal experts said he, like Sir Philip, had probably threatened a damaging tribunal case.