Last night, police said a baby’s remains were found close to where Constance Marten and her partner Mark Gordon were arrested on suspicion of child neglect on Monday.

The pair had been avoiding police for several weeks and were detained by officers in the city, but the child was not with them – sparking a widespread search.

Helicopters, sniffer dogs, drones and thermal imaging cameras were all deployed during the two-day operation.

As the investigation continued, police became more concerned the child had come to “serious harm” and the couple were rearrested on suspicion of gross negligence manslaughter.

Detective Superintendent Lewis Basford said: “It is my very sad duty to update this afternoon, police officers searching a wooded area close to where Constance and Mark Gordon were arrested, discovered the remains of a baby.”

DS Basford said a post-mortem examination would take place in due course.

Marten and Gordon refused to divulge information on the location or welfare of the baby while they were held in custody, leading to the extensive search operation.

Detectives were granted a 36-hour custody extension by a magistrates earlier yesterday.

After a car belonging to Marten (35) and Gordon (48) was found on fire abandoned near Manchester on January 5, police began a search for the couple.

Inquiries revealed Marten, who comes from an aristocratic family, had given birth just prior to the incident and had not been assessed by medical professionals.

Manchester Police established the family had left the car and the motorway safely.

They used taxis to travel to Liverpool, then Essex, and on to London, before arriving in Sussex on January 8.

The couple avoided detection by only making payments in cash, hiding their faces on CCTV and often moving around at night.

At 9.30pm on Monday, a member of the public, who recognised Marten and Gordon from media appeals, dialled 999 after spotting the pair withdrawing cash at a convenience store. Officers arrived at the scene six minutes later.

CCTV footage from just before they were caught appears to show Gordon, who served 20 years in a US jail for rape and battery, limping.

Throughout the time the couple were missing, police appealed to them to get their baby medical attention, and raised concerns that the family had been sleeping rough in freezing temperatures.

Marten’s parents had made public pleas through the media.