A 49-year-old man has been arrested on suspicion of the murders of Sharon Pickles, 45, and Clinton Ashmore, 59, who were found fatally stabbed at two addresses in Westminster last week.
The Metropolitan police said he was arrested at a London hospital on Thursday afternoon.
It is understood he is Lee Peacock, who was wanted for questioning by officers and was found by police seriously injured in a canal barge in Ealing, west London.
Police said it was believed his injuries were self-inflicted and he has since been discharged from hospital, arrested and taken into custody at a London police station.
On 19 August at 9.30pm, police were called to an address in Ashbridge Street, Westminster, where Pickles was pronounced dead.
At 2.15am on 20 August, Ashmore was pronounced dead at an address in nearby Jerome Crescent.
The Met said both had died from a stab wound to the neck and the two incidents were being treated as linked.
On Friday night, Det Ch Insp Wayne Jolley, from the Met’s specialist crime command, said: “This is a significant development in our investigation which I hope takes us a step closer to getting justice for the families of Sharon and Clinton.
“I am aware that as a result of appeals for information issued by the police, there is more information in the public domain about this case than there might ordinarily be.
“A man has now been arrested and it is crucial that nothing is said or reported that could risk prejudicing any future court proceedings.
“I would urge the public and the press to avoid speculating or sharing names or images in relation to this arrest or this investigation.”