A probe into claims Home Secretary Priti Patel bullied staff is still being "processed" eight months after it began.
No10 made the admission after a former MI5 boss demanded the Cabinet Office's findings be made public.
Lord Jonathan Evans, chairman of the Committee on Standards in Public Life, said if they were kept secret people may think the claims were being "brushed over".
But Boris Johnson 's spokesman insisted: "The PM will make any decision on the matter public once the process has concluded."
A Cabinet Office investigation was launched in March over claims Ms Patel belittled colleagues and clashed with officials.
Sir Philip Putnam, the Home Office's top civil servant, quit after accusing her of a "vicious briefing campaign".
Shadow Home Secretary Nick Thomas-Symonds said: "It is a disgrace the report is being suppressed."