A senior Scotland Yard officer could face the sack for alleged racist language after using the phrase “whiter than white” in a briefing to colleagues.

He could face an internal investigation for gross misconduct — the most serious disciplinary offence. Sources said the detective superintendent addressed colleagues about the need to be faultless and above reproach in carrying out inquiries, saying that they needed to be “whiter than white”.

The Met later received a complaint about his comment and passed it to the police watchdog for investigation.

The officer has now been placed on restricted duties while the Independent Office for Police Conduct investigates. He has been told the inquiry may take up to 12 months to complete.

A highly respected officer, he strenuously denies any wrongdoing and is co-operating fully with the investigation. He is attached to the Met’s anti-corruption squad, the Directorate of Professional Standards, a policing branch portrayed in the BBC drama Line Of Duty.

Insiders said the internal investigation shows the extent to which the police misconduct process has got out of hand.

One said: “There was no bad intent in this comment, it may have been a poor use of language but this is not what the misconduct process is for. This is not corruption, this is not serious wrongdoing. There should be informal ways of dealing with this, particularly at a time when we are so short of experienced officers.”

A spokesman for the Plain English Campaign said: “As the phrase means ‘morally beyond reproach’ and is used in that context with that intent, it seems fairly ludicrous that the officer in question is being investigated at all, let alone for ‘gross misconduct’. ”

An inquiry is believed to be running into an officer’s use of the phrase “pale, stale and male” in another force. A “good egg” is also thought to be discouraged in police ranks because it is deemed to be too closely associated with “egg and spoon”, rhyming slang for a highly offensive racist term.

The complaint involving the phrase “whiter than white” is among a number of claims levelled against officers in the Met’s anti-corruption unit in an IOPC inquiry codenamed Operation Embley. Allegations include racism, interfering in investigations and turning a blind eye to wrongdoing.

Three officers have been served with gross misconduct notices, including the superintendent accused of using the phrase “whiter than white”. Another officer is also under criminal investigation. Up to 11 others are facing possible inquiries.

Met chief Cressida Dick has not commented on the details of the allegations against officers, but said recently that it was “ridiculous” to compare the IOPC inquiry with Operation Countryman into a major Seventies bribe scandal. She said she had “total confidence” in the professional standards unit.

The allegations against the Met superintendent first surfaced in June. He is understood to have been issued with the misconduct notice as part of the usual procedure to allow him to instruct a lawyer and conduct a defence of the claims.

A Met spokesman refused to comment, saying the allegation against the officer formed part of the IOPC investigation under Operation Embley.

The IOPC said: “I can confirm that as part of Operation Embley into allegations of serious corruption and malpractice within the Directorate of Professional Standards a notice of investigation has been served on an officer informing them we are investigating the alleged use of language deliberately intended to offend and that had racist undertones.

“A notice is issued to inform an officer at the earliest opportunity following an allegation and to safeguard their interests. It in no way indicates that misconduct proceedings will take place.”

Victor Marshall, Professional Standards Co-ordinator for the Police Superintendents’ Association, said: “We are supporting an officer who is under investigation for gross misconduct.

“The officer strenuously denies any wrongdoing and is co-operating fully with the investigation.”