An officer in London's diplomatic protection branch was arrested Wednesday on suspicion of murder, police said, as investigators searching for a missing 33-year-old woman discovered human remains.

The Metropolitan Police said the officer, who is a member of the same force, was originally detained late Tuesday on suspicion of kidnapping, and is also being held on a separate allegation of indecent exposure.

The officer, aged in his 40s and who serves in the parliamentary and diplomatic protection command, remains in custody at a police station in the British capital, the Met said.

A woman in her 30s was also arrested Tuesday on suspicion of assisting an offender and remains in custody as part of the investigation, the force added.

The arrests came hours before Metropolitan Police Commissioner Cressida Dick announced that officers searching woodland near the town of Ashford, southeast of London, had found human remains.

"We are not able to confirm any identity and indeed that may take us some considerable time," she said.

Police had begun searching the woods, as well as several other sites in London and the county of Kent, earlier in the day.

The developments follow a week-long investigation into the disappearance of Sarah Everard, who vanished while walking home from a friend's flat in south London on the evening of March 3.

The marketing executive was last seen on CCTV walking alone on a street, but she never made it home, according to police, whose repeated appeals for information have received wide media coverage.

Sarah Everard went missing in south London on the night of March 3
Sarah Everard went missing in south London on the night of March 3 METROPOLITAN POLICE / -

The arrested officer, whose primary role was armed patrols of diplomatic premises, was detained in Kent on Tuesday.

Dick said the arrest had "sent shockwaves and anger through the public and through the Met".

"I speak on behalf of all my colleagues when I say that we are utterly appalled at this dreadful, dreadful news," she added.

"Our job is to patrol the streets and to protect people."

The Met's parliamentary and diplomatic protection command, known internally as PaDP, was created in 2015 and is the UK's largest armed police unit.

It is tasked with various roles involving the protection of high profile individuals and iconic sites.

The arrest of one of its officers triggered an automatic referral to the Independent Office for Police Conduct watchdog, which deals with policing complaints in England and Wales.

London mayor Sadiq Khan said in a statement he recognised people would be "shocked and worried" by the developments.

"I know how concerned the public will be at the news that a serving police officer has been arrested, and it is right that the case has been referred to the police watchdog for independent investigation," he said.