In a press conference this afternoon Detective Superintendent Lewis Basford of the Metropolitan Police confirmed that the couple have been further arrested on suspicion of gross negligence manslaughter.
The couple were arrested on suspicion of child neglect late last night in Hollingbury, Brighton, after a member of the public spotted them going into a shop in the area.
More than 200 police officers are in the process of looking for the baby, with hopes that the child will still be found safe and well.
Det Supt Basford said: “We feel the risk is getting so great we now have to consider the possibility that the baby has now come to harm.
“We still remain focused on an open land search to find the baby safe and well.”
He raised concerns for the baby’s health given the cold weather in the area.
Officers are desperately searching 91 square miles between Newhaven and Brighton.
Police said that the couple had spent a “considerable amount of time outdoors” and had a substantial amount of cash on them.
The couple had last been seen in Newhaven on January 8 before their arrest at around 9.30pm yesterday.
The pair were arrested by officers six minutes after a 999 call made by a member of the public on Monday night.
Police expressed their gratitude to the public for their cooperation as their investigation continues, with people urged to “remain vigilant” and contact 101 or 999 if they have any information that can help find the missing baby.
An increased police presence will remain in the area while the search continues.