Missing couple Constance Marten and Mark Gordon arrested ...

A couple who disappeared with their baby have been found but the infant is still missing, police have said.

Constance Marten and her partner, the convicted sex offender Mark Gordon, were located by Sussex police in Stanmer Villas in Brighton on Monday night after a member of the public reported seeing them shortly before 9.30pm.

The Metropolitan police said an urgent search operation was under way to find their baby, who has not received any medical attention since birth in early January.

Marten, 35, and Gordon, 48, have been travelling around the UK by taxi since their car was found burning 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 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 then 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. Gordon served 20 years in a US jail 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”.

In mid-January, Marten’s estranged father, Napier Marten, a film and music producer, appealed to her to hand herself in to the police. He said: “Darling Constance, even though we remain estranged at the moment, 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.”

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