An urgent search for the baby of aristocrat Constance Marten and her partner Mark Gordon has entered its second day amid growing fears for the child’s safety.

Marten and Gordon were arrested in Brighton on Monday on suspicion of child neglect after being spotted by a member of the public at about 9.30pm.

They were further arrested on suspicion of gross negligence manslaughter on Tuesday.

More than 200 police officers are looking for the child and they have been concentrating on an allotment and woodland in the city.

A helicopter, sniffer dogs, thermal cameras and drones have joined the search, which has widened to include the area towards Newhaven.

Marten, 35, and Gordon, 48, were reported missing on 5 January after their car caught fire on the M61, near Bolton.

It is believed Marten had given birth just a few days before.

They were spotted multiple times in the days that followed, including in Liverpool, Essex, south London and East Sussex.

Concerns about their baby grew as it is not thought to have had any medical care.

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Met Police Detective Superintendent Lewis Basford said the couple had not given them information about the child’s whereabouts or even disclosed its gender.

“We now have to consider the possibility that the baby has come to harm,” he told reporters.

He said he still hoped the baby could be found alive but that the cold weather was an obvious risk to its safety.

“Clearly the risk is getting higher… this may not end in the way we would like, but we need to remain hopeful,” he said.

He added they were still open-minded about the possibility the child may have been given to someone else to look after.

Chief Superintendent James Collis, from Sussex Police, said the search area was “vast” at about 91 square miles and centred on land between Brighton and Newhaven – about seven miles further down the coast.

He also appealed for people to contact the force with any information or potential sightings over the last few weeks.

Marten’s father, Napier Marten, told The Independent it was “an immense relief” to know the couple had been located but “very alarming news her baby has yet to be found”.