The mother of a missing aristocrat who vanished more than a month ago with her newborn baby and convicted sex offender boyfriend has issued an emotional open letter to her daughter.

Virginie de Selliers pledged to stand by Constance Marten, 35, and her grandchild, telling her: “You are not alone in this situation. We will support you in whatever way we can.”

Miss Marten and her partner Mark 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.

Police believe the couple are sleeping rough in a blue tent and fear for the safety of the baby, who has not had any medical attention since birth in early January.

Mark Gordon and Constance Marten
A CCTV image of Mark Gordon and Constance Marten walking through Flower and Dean Walk near Brick Lane, east London on January 7 (Metropolitan Police/PA)

In the letter, sent to the PA news agency by a representative for the family, Mrs de Selliers writes: “Open Letter to My Darling Daughter Constance.

“I know you well enough; you are focused, intelligent, passionate and complex with so much to offer the world. So many of your friends have come forward to say such positive things about you, assuring us of their warmest love and support for you and your family.

“You have made choices in your personal adult life which have proven to be challenging, however I respect them, I know that you want to keep your precious new-born child at all costs.

“With all that you have gone through this baby cannot be removed from you but instead needs looking after in a kind and warm environment.

“I want to help you and my grandchild. You deserve the opportunity to build a new life, establish a stable family and enjoy the same freedoms that most of us have.

“Constance, I will do what I can to stand alongside you and my grandchild. You are not alone in this situation. We will support you in whatever way we can.

“I am ready to do what it takes for you to recover from this awful experience so you can thrive and enjoy motherhood.

“I love you and miss you, Mum xx.”

It is the first time that Miss Marten’s mother has said anything publicly about her daughter’s disappearance.

The missing couple have so far avoided being traced by the police by moving around frequently and keeping their faces covered in CCTV images.

Mark Gordon
Mark Gordon has been missing with Constance Marten and their baby since January 5 (Greater Manchester Police/PA)

A £10,000 reward is on offer for information that leads to them being found safe.

Investigators said that in the months before they vanished they built up a significant amount of cash and used it to pay for places to stay and taxis around the country.

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.

In an update on Sunday, the Metropolitan Police said they believe the family may be camping in Sussex.

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

Since then the couple have led an isolated life, and in September, when Miss Marten was well into her pregnancy, began moving around rental flats.

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

Anyone with information can call the incident room on 020 7175 0785 or Crimestoppers anonymously on 0800 555 111.