The police watchdog is investigating a series of "grossly offensive" WhatsApp messages, said to be "discriminatory, derogatory or pornographic" in nature.

Five of the officers work for the Civil and Nuclear Constabulary.

The ex-officer also used to work for the unit, which polices nuclear sites.

The other person involved has since moved to another force in south-west England.

All seven are being investigated over "grossly offensive messages" under the Communications Act said the Independent Office for Police Conduct (IOPC), which is responsible for carrying out the inquiry.

The officers have also been told they are under investigation for potential gross misconduct, although it does not mean criminal charges or misconduct proceedings will follow.

IOPC regional director Catherine Bates said: "The allegations against these officers and a former officer are extremely serious and concerning.

"On conclusion of our investigation we will decide whether the matters should be referred to the Crown Prosecution Service, whose role it is to determine whether criminal charges will follow."

The status of each officer will remain under review throughout the investigation, the IOPC said.

The probe was launched after information came to light in a separate police investigation.

But the case is not linked to any ongoing or former investigations into police WhatsApp messages.

Metropolitan Police Commissioner Sir Mark Rowley has announced plans for a new anti-corruption unit to crack down on officers who carry out abusive behaviour.

Speaking to Newsnight on Thursday, Sir Mark promised cultural reform, saying he would "root out" corrupt officers and staff from the organisation through a new anti-corruption and abuse command.

The 100-strong team will investigate police who are "predatory, who abuse their position of trust - for their personal, financial or sexual advantage - whether on duty, off duty, in person or online", he said.