Detectives attempting to find Constance Marten’s baby have said the risk to the infant’s welfare is “as high as it’s been in the investigation” as they search the Sussex undergrowth.

The aristocrat and her partner Mark Gordon were arrested in Brighton on Monday on suspicion of child neglect after several weeks avoiding the police, but the child was not seen with them.

The couple were detained after a 999 call by a member of the public who had seen media reports about the pair.

Since Marten and Gordon were arrested, more than 200 police officers have been engaged in the search for the two-month-old baby, using sticks to wade through bushes in woodland near Stanmer Villas and Golf Drive.

The infant was born in early January and has had no medical attention since then, with his parents sleeping rough in freezing temperatures much of the time.

The senior investigating officer, Detective Superintendent Lewis Basford, said police were making assessments on the baby’s welfare “on the hour, by the hour”.

He said nothing significant has been found, including items such as a tent bought at Argos on January 7, adding: “We would still say we are actively looking for those.”

Mr Basford told reporters: “We have got nobody who has actually physically seen the baby.

“We’re still in a position where we hold hope that the baby is safe and well.

“We agree that the risk is extremely high – probably as high as it’s been in the investigation.

At no point have we seen, in that short period of CCTV... that they allowed others to have that baby

“Clearly, as it’s fast moving, we’re making assessments on the hour, by the hour, as to what our hypotheses are around the ongoing welfare of the baby.”

Asked if the couple could have given the baby to somebody else, Mr Basford said: “Certainly our main line of hypothesis is that they (Marten and Gordon) were in control and custody of the baby.

“At no point have we seen, in that short period of CCTV… that they allowed others to have that baby.

“In fact that baby was very much concealed within the coat lining of Constance or in the buggy for the short period they had it.”

Mr Basford said officers “could not rule out” that the couple had found someone “like-minded or who does not conform or appreciate the establishment” and used the money they had for “safe lodging”.

He added that after the arrests, this line of inquiry did not become “as significant”.

Marten and Gordon are being assessed on their fitness to be interviewed and to be detained, Mr Basford said.

They were arrested by officers six minutes after the 999 call was made.

Marten’s father said it is a huge relief that his daughter has been found, but it is “very alarming” that her baby remains missing.

Napier Marten told the Independent he loves his daughter but it would have been “far better” if she and Gordon had handed themselves in earlier.

Mr Napier told the newspaper: “It is an immense relief to know my beloved daughter Constance has been found, tempered by the very alarming news her baby has yet to be found.

“For whatever reasons she and her partner went on the run, the consequences of their actions have increased many fold. It would have been far better if they had handed themselves in earlier.

“When the time comes, I am longing to see Constance to reassure her that, whatever the weather, I love her dearly and will support her as best I can through the difficult weeks and months here on in.”

The police search for Marten, 35, and Gordon, 48, began on January 5 when their car was found on fire abandoned next to the M61 in Bolton.

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.

They were finally arrested at about 9.30pm on Monday.

Marten, who is from a wealthy aristocratic family, was a promising drama student when she met Gordon in 2016.

Since then the couple have led an isolated life, and in September, as Marten’s pregnancy progressed, began moving around rental flats.

Gordon served 20 years in prison in the US for rape and battery committed when he was 14.

It is unknown if their baby was full-term or has any health issues.

In an appeal a week ago, Shereen Nimmo, director of midwifery for Barts Health NHS Trust, urged the couple to bring the baby in for checks.

She said: “You’re putting your baby at risk by not accessing medical care, so it’s really important that you come and see a midwife, doctor or another healthcare professional as soon as possible.

“Babies need a safe, warm environment and all new mums are given information about safe sleeping for their baby to prevent sudden infant death syndrome.

“Please do the right thing for your baby and go to your nearest healthcare facility so my caring colleagues can take care of you and your baby. All we want to do is help you.”

Anyone who may be able to assist in the search for the couple’s baby is urged to contact 999.