A renewed appeal to help find a missing aristocrat who vanished more than a month ago with her convicted sex offender boyfriend and their newborn baby has been issued.

Detectives from the Metropolitan Police have appealed to the public once again to report any sightings of Constance Marten, 35, and Mark Gordon, 48, to the police.

It is now more than six weeks since the car the pair was travelling in was found on fire on the hard-shoulder of the M61 on Thursday, January 5.

It is believed Constance gave birth either in or near the car only a day or two earlier.

Neither the baby nor Constance have received any medical attention. It is unknown if the baby was full-term or has any health issues, which is why officers remain committed to finding the family, the Met said.

The last confirmed sighting of them was at about 06.15am on Sunday, January 8, when they walked along Cantercrow Hill, in Newhaven, into the fields beyond.

However, given the time that has passed they could have moved on some considerable distance since then, police said.

Detective Superintendent Lewis Basford of the Met’s East Area Command said: “We’ve been working around the clock behind the scenes and we’ve viewed more than 630 hours of CCTV as part of our efforts to find them.

“Information from the public has been vital to our investigation and we have received more than 350 calls to our dedicated incident room – thank you to everyone who has made contact with us so far, we are so grateful to you.

“While sadly these calls have not yet led to the couple and their baby being found, it could take just that one call into us with the right information, at the right time, to help us find the family and make sure they are okay.

“We are continuing to offer a reward of up to £10,000 for any information that leads to the family being found.

"So please, if you have information and have not yet come forward or if you think you have seen them, please contact the incident room without delay.

“They could be absolutely anywhere in the UK, so we need everyone to remain vigilant.

"When they were last sighted on January 8 they were in the possession of a blue two-man tent, so please keep your eyes peeled, especially while you are out and about in waste ground or beauty spots, or while you’re walking the dog.

“Please be mindful that they might not always be out and about together.

“I would like to stress that we are not doing this and putting so many resources and efforts into finding the family just to be awkward or to interfere. We have a genuine concern for the health and wellbeing of the baby, and Constance and Mark, and it our duty to ensure that they are okay.”

Anyone who has information on the family’s whereabouts can call the incident room on 020 7175 0785.

Alternatively, information can be reported anonymously to the independent charity Crimestoppers on 0800 555 111.

Lewes police have been appealing to anyone who may have seen them in the Newhaven area.