A couple who went missing with their baby have been found, but the infant remains missing, according to police.

Sussex police apprehended Constance Marten and her partner, convicted sex offender Mark Gordon, in Brighton’s Stanmer Villas on Monday night after a member of the public reported seeing them shortly before 9.30 p.m.

The Metropolitan Police Department said an urgent search was underway to find their baby, who had not received medical attention since his birth in early January.

Marten, 35, and Gordon, 48, have been taking taxis around the UK since their car caught fire on the M61 in Bolton, Greater Manchester, on 5 January.

Authorities previously believed the couple had been sleeping rough in a blue tent and had avoided being tracked down by police by moving around frequently and hiding their faces from CCTV.

Constance Marten and Mark Gordon Missing Couple With Baby
Mark Gordon and Constance Marten have been travelling around the UK since their car was found burning on the M61 in Bolton on 5 January.

The couple traveled from Bolton to Liverpool, then to Harwich in Essex, east London, and finally to Newhaven in Sussex, where they were seen near the ferry terminal on January 8.

Marten comes from a wealthy aristocratic family with royal connections, and he was a promising drama student before meeting Gordon in 2016. Gordon served 20 years in a US prison for rape and battery for an attack on a woman when he was 14, and was deported to Britain from the US in 2010.

Since 2016, the couple have led an isolated life cut off from family and friends. From about September last year, they began living in a series of Airbnbs around the country on short lets 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 unknown if their baby was full-term or has any health issues.

In late January, police offered a £10,000 award for information leading to the couple’s whereabouts. At the time, officers said they were extremely concerned about the health and wellbeing of the newborn baby, adding they may have been “exposed to sub-zero temperatures, for almost a month now”.

Marten’s estranged father, Napier Marten, a film and music producer, pleaded with her to turn herself in to police in mid-January. “Darling Constance, even though we are currently estranged, I stand by, as I have always done and as the family has always done, to do whatever is necessary for your safe return to us,” he said.

Constance Marten grew up on the Crichel House estate in Dorset. Her grandmother was Princess Margaret’s playmate, and her father was once a page to Queen Elizabeth II.