The police watchdog is investigating allegations of "serious corruption and malpractice" within Scotland Yard's own standards unit, a director has said.
The Independent Office for Police Conduct (IOPC) is probing claims of "potentially conflicted" senior officers in the Metropolitan Police's anti-corruption unit.
Its investigation will examine whether officers within the Directorate of Professional Standards (DPS) unit - subject of the BBC drama Line of Duty - interfered with or curtailed investigations or failed to look at alleged wrongdoing altogether.
Jonathan Green, the IOPC's London director, said the watchdog was also investigating claims of racial discrimination in the DPS, which is tasked with tackling misconduct and corruption in the UK's largest police force.
So far, gross misconduct notices have been served on three officers, one of whom is also under criminal investigation, while "a number of officers" are also being assessed.
Scotland Yard said it was "fully co-operating" with the IOPC's investigation into allegations against "a number of MPS (Metropolitan Police Service) personnel".
Mr Green told The Sunday Times: "I can confirm we have begun an investigation into allegations of serious corruption and malpractice within the Directorate of Professional Standards of the Metropolitan police.
"The investigation includes alleged interference in, and curtailment of, investigations by potentially conflicted senior officers, failure to investigate allegations of wrongdoing, systemic removal of the restrictions of officers under investigation and racial discrimination.
"As part of this investigation three officers have been served with gross misconduct notices and one of those officers is also under criminal investigation. Assessments on the status of a number of other officers remains ongoing."
According to The Sunday Times, three whistleblowers from the force approached the IOPC to allege members of the DPS were shielding officers from a range of allegations.
A Scotland Yard spokesman said: "The Metropolitan Police Service has referred allegations regarding the conduct of a number of MPS personnel to the IOPC which is conducting an independent investigation.
"The MPS is fully co-operating with the IOPC investigation."