LONDON (AFP) - British police said on Thursday (March 11) they had been granted more time to question a fellow officer, serving in London's diplomatic protection branch, arrested on suspicion of kidnapping and murdering a missing woman.

The Metropolitan Police said the officer, who is a member of the same force and in his 40s, was in custody at a facility in the capital after a magistrates' court approved his continued detention.

Police said the officer under suspicion was treated in hospital on Thursday for a head injury sustained while in custody but had since been returned to a police station.

The Sun newspaper reported he was found collapsed and unconscious in his cell after suffering head wounds.

The latest developments in the high-profile probe into the disappearance of Sarah Everard came 24 hours after the discovery of human remains in woodland in Kent, south-east England.

Police have said it may take "considerable time" to identify the remains, but fears have grown that they are the corpse of the 33-year-old marketing executive.

She has not been seen since vanishing while walking home from a friend's flat in south London on the evening of March 3.

Prime Minister Boris Johnson on Thursday expressed his shock at the case, which has sparked renewed debate in Britain about women's safety in public spaces.

"I am shocked and deeply saddened by the developments in the Sarah Everard investigation," said Johnson.

"Like the whole country my thoughts are with her family and friends. We must work fast to find all the answers to this horrifying crime."

'Kind and strong'

The Met announced on Wednesday that the officer, a member of its elite diplomatic protection branch, had been arrested on suspicion of murder, sending shockwaves around the country.

The suspect, whose identity has not been released by officials but has been widely named in the media, was originally detained in Kent late Tuesday on suspicion of kidnapping.

He is also being questioned on a separate allegation of indecent exposure.

A woman in her 30s arrested at the same time as him late on Tuesday, on suspicion of assisting an offender, has been released on bail, the Met added.

Metropolitan Police Commissioner Cressida Dick said Wednesday that the arrest had prompted "waves of shock and anger through the public and through the whole of the Met".

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

Everard's family released a statement through police Thursday describing her as a "shining example" of a "kind and strong" person, and appealed for anyone with information to come forward.

"Our beautiful daughter Sarah was taken from us and we are appealing for any information that will help to solve this terrible crime," they said. "No piece of information is too insignificant."

A vigil, under the slogan "Reclaim These Streets", will take place Saturday on Clapham Common, where it is believed Everard was walking just prior to her disappearance.

Organisers of the event on social media have said: "In Clapham, police told women not to go out at night this week. Women are not the problem.

"This is a vigil for Sarah, but also for all women who feel unsafe," they added.