A couple who disappeared with their baby have been arrested on suspicion of gross negligence manslaughter, as officers searching for the child say fears are growing for its safety. Constance Marten and her partner, Mark Gordon, have not told police the location of the infant or even its sex since being arrested on Monday. Police said on Tuesday that, as the period the child has potentially been exposed to the winter weather approached 24 hours, they had to take increasingly seriously the possibility that, as a minimum, its life is in imminent danger. The couple were found by Sussex police at Stanmer Villas in Brighton on Monday night after a member of the public reported seeing them shortly before 9.30pm. They were initially arrested on suspicion of child neglect and further arrested on suspicion of manslaughter on Monday, officers have said. The Metropolitan police emphasised that officers had no specific information to indicate the child had come to serious harm. But they struck a pessimistic tone as they updated reporters early on Tuesday evening. An urgent search operation is continuing efforts to find the baby, who is believed to have received no medical attention since birth in early January, with police urging the public to look for signs of the infant, including in sheds and outhouses. The senior investigating officer, DS Lewis Basford, said: “I can confirm that they were initially arrested on suspicion of child neglect. I can now confirm that they have been further arrested on suspicion of gross negligence manslaughter and that they remain in custody at police stations in Sussex. “The baby was not with them, and we have not found the baby as yet.” He had earlier told reporters on a conference call the couple had not provided any information that would help locate their baby. Basford said that a member of the public, after media reporting of images of the couple, saw them withdrawing cash outside the Mulberrys convenience store on Hollingbury Place in Brighton shortly after 9.30pm on Monday. He added the couple were heavily clothed for outdoor activity. It took six minutes from the member of the public calling 999 and the police arresting the couple, on the corner of Golf Drive and Stanmer Villas. As of 2.30pm on Tuesday, the Met had more than 200 officers deployed to Sussex alongside significant resources from Sussex police. Marten and Gordon were living outdoors before they were found, Basford said. He told reporters on Tuesday: “Working hypothesis still remains that we believe them to have been in the open land and open areas, that is why our focus and our search is where it is. “We are conscious to the fact that there are outbuildings, it’s a vast amount of land.” Basford said that while there was still hope of finding the baby, as “time passes we are against the clock due to the risk posed by the climate and weather conditions”. “From both of those at this time in custody we have not as yet got any further information as part of the investigation,” he added. Detectives were open to the possibility the baby may have been handed to someone else, but they believe this is less likely, Basford said. Neither of the arrested parents were wanted for any offences before their disappearance. Dozens of officers were seen searching Hollingbury golf course and Roedale valley allotments on the Sussex Downs. Police officers at the allotments were seen bagging up a pair of child’s pink earmuffs. After the arrests, Marten’s estranged father, the film and music producer Napier Marten, told the Independent: “It is an immense relief to know my beloved daughter Constance has been found, tempered by the very alarming news her baby has yet to be found.” The couple had been travelling around the UK by taxi since their car was found burning on the M61 outside Bolton, Greater Manchester, on 5 January. Authorities previously believed they had been sleeping rough in a blue tent, and had avoided being traced by the police by moving around frequently and keeping their faces covered from CCTV. The couple travelled from Bolton to Liverpool, then to Harwich in Essex, to east London and to Newhaven in Sussex, where they were seen near the ferry port on 8 January. Marten is from a wealthy aristocratic family with connections to the royal family and was a promising drama student before meeting Gordon in 2016. Since 2016, the couple have led an isolated life, cut off from family and friends. From about September last year, they began living on short lets in a series of Airbnbs around the UK and amassed a significant amount of cash to enable them to live off-grid and avoid the attention of the authorities. Taxi drivers used by the couple in the first few days after they went missing said they had heard noises coming from a baby. It is not known whether their baby was born full-term or has any health problems. In late January, police offered a £10,000 award for information leading to the couple’s whereabouts. Marten grew up at Crichel House, an estate in Dorset. Her grandmother was a playmate to Princess Margaret and her father was once a page to Queen Elizabeth II.