A serving Metropolitan Police officer has been arrested in Kent following the disappearance of Sarah Everard.
The force says he was detained at a property last night - along with a woman who is being held on suspicion of assisting an offender.
Sarah, 33, went missing in south London last Wednesday evening as she walked home from Clapham Junction to Brixton.
Police investigating her disappearance say the man and woman are being questioned at a station in London.
The Directorate of Professional Standards is aware, and Sarah's family has been kept updated of the developments.
Speaking this morning, Met Police Assistant Commissioner Nick Ephgrave said the officer, who remains in custody at a London police station, was not on duty at the time of Sarah's disappearance.
The woman who was arrested at the same time and same location as the officer also remains in custody this morning.
He described the fact that the man arrested was a serving officer as "shocking and deeply disturbing", adding: "As a father myself of four young woman I can only imagine the anguish Sarah's family is feeling at this very difficult time."
He did not confirm what the officer had been arrested on suspicion of.
Detective Chief Inspector Katherine Goodwin, in yesterday's statement, said: “This is a significant development in our inquiry. This is a fast moving investigation and we are doing everything we can to find Sarah.
"We have seen an overwhelming response from the public and I repeat my request for anyone with information that may be relevant to come forward, no matter how insignificant it may seem."
Last night, Mr Ephgrave said: "The arrest this evening is a serious and significant development. We will continue to work with all speed on this investigation but the fact that the arrested man is a serving Metropolitan Police officer is both shocking and deeply disturbing.
"I understand there will be significant public concern but it is essential that the investigative team are given the time and space to continue their work."
The news comes amid a police search being carried out in a wooded area in an undisclosed location. The search involves specialist search dogs.
The arrest came later on the same day that the father of Sarah's boyfriend Josh Lowth pleaded for information from the family home in Kent.
Josh's father Chris, who lives in Sidcup, said: "We are concerned, like everybody is. We really, really want to see her back.'
"The whole family is obviously very worried about her and just wants her home safely.
"We're all pulling together and praying that this awful situation is quickly resolved. We want to thank the media for all their help."
Ms Everard is thought to have walked through Clapham Common towards her house in Brixton – a journey which should have taken around 50 minutes.
She was last captured on a doorbell camera walking along the A205 Poynders Road towards Tulse Hill at around 9.30pm.
On Tuesday evening, police put up a cordon outside a block of flats near where the footage was recorded.
The search was focused on the Poynders Court housing complex on Poynders Road, and forensics officers could be seen examining the area.
Sniffer dogs were also used to search the nearby Oaklands Estate and gardens in surrounding streets, while other officers were lifting covers and searching drains along the A205.
The Met said it had received more than 120 calls from the public and had visited 750 homes in the area as part of the investigation.