More than 300 unaccompanied children living in the Calais refugee camp could be eligible for sanctuary in the UK, a leading charity said today, as more than 60 faith leaders urged the British government to take immediate action.

Since March this year, around 40 refugee children from Calais have been reunited with their families in the UK, and 76 more have live legal cases.

However Citizens UK, which has been working on a reunion programme, said that 300 more could be eligible to legally live in Britain under the recent Dubs amendment to the Immigration Bill.

Tabled by Labour peer Lord Alf Dubs, the amendment means that unaccompanied refugee minors in Europe can be relocated to the UK, though no children have so far arrived under the scheme.

Lord Dubs, who arrived in the UK as a refugee fleeing Nazi Germany in 1939, condemned the failure of the British government to provide sanctuary to children in desperate need.

"It is a national embarrassment that refugee children who have a legal right to sanctuary in the UK are still living in tents in Calais," he said.

"They have been through unimaginable hardship on their lone journeys through Europe, and now face losing their makeshift homes as the French authorities threaten to bulldoze the northern area of the camp. The British Government must act to end the suffering of these children."

The new figures from Citizens UK follow the announcement by the mayor of Calais, Natacha Bouchart, on Monday that the remaining half of the so-called 'Jungle' refugee camp will soon be torn down, leaving thousands homeless.

The Calais prefecture is expected to offer more information on the planned demolitions on Thursday.

According to charity Help Refugees, there are 608 unaccompanied children living in the northern section of the camp, which is under threat. 

After the southern section of the Jungle was torn down in February, 129 unaccompanied minors went missing. Co-founder of Help Refugees, Josie Naughton, said "that is sure to happen again unless British officials act to ensure these children are protected.

"There are 10,000 children who have reportedly gone missing in Europe so far," she added. "This demolition would add hundreds more to that terrible tally."

Bishop of Durham, Paul Butler, urged French officials to delay the demolition "until the children have been processed and reunited with their families.

"Evicting the children will only force them into the hands of traffickers or onto the train tracks," he warned.

A letter signed by more than 60 faith leaders in The Times today echoed this call.

"When the police demolished the southern area of the camp earlier this year, children were put in immense and unnecessary danger, hundreds went missing, many forced into the hands of traffickers or stowing away in vehicles. This time it is likely to be worse, with no section of the camp left to retreat to and the government-provided bed spaces completely occupied," the letter read.

"Today, over 60 faith leaders from the Jewish and Christian communities are calling on the authorities to stop the demolitions until all the children with a full legal right to be in the UK have been transferred and the remaining children have been safeguarded. Theresa May has seen this situation develop as home secretary. It would be admirable if one of her first acts as prime minister was to show the moral leadership this desperate situation demands."

The letter was signed by the Archbishop of Birmingham, Bernard Longley, as well as the bishops of Southwark, Manchester, Croydon, Barking and Dover .

Lily Caprani, deputy executive director at Unicef UK, branded reports of the upcoming eviction "deeply worrying".

Hundreds of children will be left destitute, she warned, "many of whom have a right to be reunited with family in the UK. This will cut off any hope of a safe and legal route, which they're entitled to, and effectively drive them onto the train tracks and into the backs of lorries.

"For the refugees who've left their homes fleeing conflict, these reports must come as another blow to their hopes of reaching safety. If any eviction does go ahead, there must be robust plans to safeguard the hundreds of children currently stranded in the camp." 

A report released last month by Unicef France and Unicef UK found that sexual violence and forced prostitution is a constant threat for children in refugee camps in Northern France, including Calais.

Some young women have exchanged sex for the promise of passage to the UK, researchers said, and children must pay an "entry fee" before they are even allowed to live in the camps. Unaccompanied minors are forced into labour if they can't afford to pay. 

Theresa May pledged in May to speed up the process of bringing eligible refugee children over to the UK, but Unicef said in June that so far "nothing ha[d] changed".