Remains have been found in an area of woodland following a major search for Constance Marten’s two-month-old baby.

Hundreds of officers from the Metropolitan Police and Sussex Police, as well as search and rescue volunteers, scoured 90 square miles of land near Brighton over the course of two days in search of the infant.

On Wednesday evening, Detective Superintendent Lewis Basford told reporters a baby’s remains had been found close to where 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 on Stanmer Villas in the city, but the child was not with them – sparking a widespread search in the Sussex undergrowth.

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 eventually rearrested on suspicion of gross negligence manslaughter.

Confirming the discovery at Sussex Police headquarters, DS 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.

“A crime scene is in place and work at the location is expected to continue for some time.

“This is an outcome that myself and that many officers who have been part of this search had hoped would not happen.

“I recognise the impact this news will have on many people who have been following this story closely and can assure them that we will do everything we possibly can to establish what has happened.”

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 Brighton magistrates earlier on Wednesday.

After a car belonging to Marten, 35, and Gordon, 48, was found on fire abandoned next to the M61 in Bolton on January 5, police began a lengthy search for the couple.

Inquiries revealed Marten, who comes from an aristocratic family with royal connections, had given birth recently – possibly one or two days before the incident – and had not been assessed by medical professionals.

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

They used taxis to first travel to Liverpool, then Harwich in Essex, and on to east 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 or in the early hours of the morning.

At around 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 in Hollingbury Place.

Officers arrived at the scene and detained the couple 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 and using a large stick to walk.

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.

Both Marten’s parents made public pleas through the media, and police offered a £10,000 reward for information leading to the couple being found.

The Sun reported that Marten and Gordon used Brighton food bank last Wednesday, but did not ask for baby supplies – which were available – and did not have the baby with them.

They also did not buy any baby supplies from a convenience store shortly before they were arrested.