POLICE searching for the missing baby of Constance Marten and Mark Gordon have said they must consider the possibility of ‘serious harm’.

The couple, who avoided police for 53 days before being arrested on Monday, February 27, remain in custody and investigators have applied for a 36-hour extension to hold them for further questioning.

They were arrested on suspicion of gross negligence manslaughter.

Providing an update on their searches, Detective Superintendent Lewis Basford told reporters: “This is a hugely difficult and painstaking search operation, covering a vast area of some 90 square miles.

“We’re using every resource we have at our disposal to find the baby.”

He added that officers ‘must consider that the baby has come to serious harm’ and urged the public to remain vigilant and continue providing information to the investigation team.

Metropolitan and Sussex police are using helicopters, sniffer dogs, thermal imaging cameras and drones, and teams will continue to work in the coming days.

Marten, 35, who comes from an aristocratic family in Dorset with royal connections, first went missing with sex offender boyfriend Mr Gordon, 48, when their car was found abandoned and on fire at the edge of the M61 on January 5.