Police are still searching for the baby of runaway aristocrat Constance Marten and her rapist lover Mark Gordon – and have applied for 36 hours more to quiz them.

The Metropolitan Police, which is leading the search in Brighton with hundreds of officers, said again today it 'must consider that the baby has come to serious harm'.

The size of the area being scouring suggests neither Marten, 35, or Gordon, 48, has disclosed the newborn's location under interview following their arrests on Monday. 

Detective Superintendent Lewis Basford said: 'This is a hugely difficult and painstaking search operation, covering a vast area of some 90 square miles. We're using every resource we have at our disposal to find the baby.'

He urged the public to remain vigilant and continue providing information to police.

The baby has never been pictured, but two taxi drivers who ferried the couple early in January said they had been able to see the shape of the infant moving and hear it crying during the journeys. 

They were later seen looking 'shifty' at a food bank near Brighton a week ago as they picked up supplies without their child. 

'She was putting the food in bags and he was standing back. I said, ''Are you together?'', but he was standing back they looked a bit shifty,' a food bank worker told The Mirror.

Today, hundreds of officers and volunteers from the London Search and Rescue charity did sweeps of Moulsecoomb Wild Park in Brighton, using sticks to look under bushes and behind trees.

By midday, members of the team had been on shift for 14 hours, and had walked eight miles.

Residents say they think they saw the couple in the area hours before their arrest. 

Lee Wright, 29, told The Times he saw a man matching Gordon's appearance walking alone towards a group of allotments holding a suitcase.

Marten and Gordon were re-arrested on Tuesday on suspicion of gross negligence manslaughter.

Det Supt Basford said it was possible the baby had 'come to harm' because the couple had refused to reveal its location despite being questioned for a 'significant period of time'.

A member of the public, who had seen media reports about the pair, phoned 999 after seeing them withdraw cash from a convenience store in the city's Hollingbury Place shortly before 9.30pm on Monday. Police arrested them within six minutes of the tip-off.

The couple were heard having a row as they walked along Stanmer Villas just before their arrest, exclusive footage obtained by MailOnline showed. 

Marten was apparently tearful when officers swooped on adjoining Golf Drive and yelled at officers to 'get off' her lover when he was restrained, saying she was worried about his mental health. 

One witness claimed he struggled and took 40 minutes to be subdued. Another said he was very angry and was shouting.

Today, a search dog van was seen making its way into Golf Drive, which leads to the allotments that have been a focus of the police search.

A number of marked police vehicles were stationed along the street and a uniformed officer stood guard at the bottom of the road.

More than 200 officers have been searching for the baby, from where the couple were last sighted to where they were arrested, including allotments and woodland.

Det Supt Basford said police still hoped to find the child safe, with a helicopter, sniffer dogs, thermal imaging cameras and drones being used in the search.

However, when he confirmed yesterday that Marten and Gordon had been re-arrested on suspicion of gross negligence manslaughter, Det Supt Basford said police had to consider the possibility the baby had 'come to harm'.

He said officers had received no information about the welfare or location of the child since the pair were detained.

Mr Basford added: 'We have had a significant period of time in custody facility with both Constance and Mark.

'At this time we have not furthered that information, which has now obviously led to the position where we feel that the risk is getting so great that we now have to consider the possibility that the baby has come to harm.

'I can now confirm that they have been further arrested on suspicion of gross negligence manslaughter and that they remain in custody at police stations in Sussex.

'The baby was not with them and we have not found the baby as yet.'

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

Inquiries revealed Marten had given birth recently, possibly one or two days before the incident, and had not been assessed by medical professionals.

Greater Manchester Police established they had left the car and motorway safely.

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.

Mr Basford said officers are looking into footage shared online of Gordon seen with a stick before he was arrested, adding that there was sufficient intelligence to suggest the pair had spent most of their time in outdoor open spaces while avoiding police.

He conceded the cold weather meant detectives had to be open to the investigation not 'ending in the way we would like'. The couple have been sleeping rough in freezing temperatures for much of the time.

Mr Basford said police are yet to locate items bought by Marten and Gordon at Argos on January 7, adding: 'We would still say we are actively looking for those.'

Meanwhile, Marten's father said it was a huge relief that his daughter had been found but it was 'very alarming' that her baby remains missing.

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

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

Since then the pair 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 child 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.

'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 help in the search for the baby is urged to contact 999.