The father of Constance Marten has 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 dearly but it would have been "far better" if she and boyfriend Mark Gordon had handed themselves in earlier.

The couple were arrested on Monday on suspicion of child neglect in Brighton after several weeks avoiding the police.

A huge search is under way in Sussex for the couple's two-month-old baby, who 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.

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."

He thanked the member of the public who tipped off police about the couple's whereabouts, as well as Metropolitan police officers for their "dogged investigation".

Napier Marten, a film and music producer, is the son of Mary Anna Marten, a British Museum trustee whose godmother was the late Queen Mother, and who used to own the Crichel estate in Dorset.

Mr Marten added: "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 Miss Marten, 35, originally from Dorset, and Mr 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 onto east London, before arriving in Sussex on January 8.

The couple avoided detection by only making payments in cash, hiding their faces when 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 on suspicion of child neglect by officers from Sussex Police.

The couple were held in Stanmer Villas, Brighton, after a tip-off from a member of the public, but the baby was not with them.

The Senior investigating officer, Detective Superintendent Lewis Basford, told BBC Breakfast that officers from the Metropolitan and Sussex police forces are searching a huge area of land to try to find the infant.

He said: "It is a vast area and, at present, we are looking in the local vicinity to where the couple were arrested last night, seeking a shelter or location for where they may have been holed up and hopefully where the baby is present.

"The arrest location was close to open land and the couple were moving towards that land. And that's why we are focusing heavily on where we are right now.

"We know that they travel, we know they travel long distances.

"My plea to the members of the public here in Brighton and crossing over towards Newhaven is please be vigilant in the open land where you are, in the outbuildings that you may have on your own property, and assist us in that way by being vigilant."

Marten, who is from a wealthy aristocratic family, was a promising drama student when she first 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."

At the time, Mr Basford said about 50 officers were working on the case at any one time and more than 630 hours of CCTV had been viewed.

He said there had been more than 350 calls to police from the public with information following previous appeals.

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