A huge search is under way for a two-month-old baby after missing aristocrat Constance Marten and her sex offender boyfriend Mark Gordon were arrested in Brighton.

The couple have been avoiding police since the infant was born in early January, moving around the country, paying for everything in cash and covering their faces when on CCTV.

They were finally arrested at around 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.

Constance Marten's family were the previous owners of Crichel Estate in Dorset, and her father, Napier Marten, was a page to Queen Elizabeth.

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.

The couple are known to have travelled long distances during the time they have been missing and the BBC reported they were seen in Newhaven a few days ago.

Mr Basford 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, 35, and Gordon, 48, have been travelling around the UK by taxi since their car was found burning on the M61 in Bolton, Greater Manchester, on January 5.

The couple travelled from Bolton to Liverpool, then to Harwich in Essex, then to east London and then to Newhaven in Sussex, where they were seen near the ferry port on January 8.

They spent time sleeping rough in a blue tent, often moving around at night and in the early hours of the morning to avoid detection.

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 around 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 ble to assist in the search for the couple's baby is urged to contact 999.