From a distance, he seemed strangely well fed for a child who had been travelling alone for 18 months. Closer, it became evident that Hassan was only trying to stay alive. Wrapped around the 16-year-old’s slender frame were seven coats. The outer layer, a quilted puffer jacket, engulfed him.

It was on Tuesday, just before 6pm as the temperature tumbled in central Paris, when the young Somalian was found shivering on the Avenue de Flandre, close to the Gare du Nord.

For four weeks he had survived penniless in Paris, sleeping on pavements in the 10th arrondissement and, when it rained, jostling for a space beneath the Stalingrad metro bridge. “People from all over Africa were gathered there, but you have to hustle for a place to sleep and the police kick people,” he said, managing a rueful smile.

Hassan left Mogadishu in July 2015, travelling alone through Kenya, Sudan, Egypt before crossing the Mediterranean in a 12-day odyssey that “made me certain I would never survive”.

His ambition had been to reach Calais and, from there, Birmingham where his eldest sister lives. Entering France, he learnt that the vast refugee camp at Calais had been demolished and so he wound up in the French capital. There is no back-up plan: “My sister is all I have.” Hassan’s father died in the continuing Somali civil war. Later, his mother was killed in a terrorist attack by al-Shabaab militants.

The teenager was found last week by Laura Griffiths of Safe Passage, which has a team of volunteers combing the French capital for child refugees who, like Hassan, are eligible to enter the UK.

Throughout 2016, Safe Passage, founded last year by the social action charity Citizens UK, has ensured that hundreds of unaccompanied child refugees have found safe and legal routes to the UK, defeating the Home Office in the high court and helping force a reticent British government to honour its political and ethical obligations.

Jamail, 14, in Paris. He fled the Taliban in Afghanistan and hopes to be reunited with his brother in Northampton. Photograph: Mark Townsend/The Observer

No one knows how many unaccompanied children are living rough in Paris, hidden in central squats or the city’s peripheral housing projects. More child refugees, many of whom are eligible to enter Britain, arrive daily in Paris. Tracking them down quickly is essential, says Griffiths.

Hassan was so vulnerable that when Griffiths found him, a man she assumed was his father turned out to be a stranger who had known him for 10 minutes.

“It is difficult though; we’re not going to find 300 unaccompanied minors with family in the UK in a week like we did in Calais. We found three yesterday, all hungry and cold and unable to speak English,” said Griffiths.

One of those previously plucked from the city streets was Jamil, an Afghan boy with neatly combed hair and a fragile coating of bumfluff above his top lip. The 14-year-old arrived in the city three weeks ago after hearing Calais was no more. Nights were spent sleeping on wasteland near the Gare de L’Est. “I would see other refugees and lie beside them. I didn’t know where to go, it was very cold. Somehow I lived,” he said, shrugging. His journey to Paris had involved traversing icy Afghan mountain passes and Persian deserts. “I walked for hours and hours, days, without food and water,” he said. For six months Jamil travelled with the sole objective of being reunited with his elder brother in Northampton.

Another brother who took the same route before him has disappeared. Returning home is not an option for Jamil. His father, a senior Taliban commander, wanted his youngest son to follow in his footsteps. “I was really frightened, I didn’t want to fight. I told my mother, who was beaten many times by my father, that I wanted to escape.” She surreptitiously sold the family’s gold jewellery to help Jamil escape. He has not heard from her since then.

For the child refugees stranded in France but entitled to enter the UK – estimated to be as high as 2,000 – it promises to be a disquieting Christmas. “The Home Office is not providing information, the children haven’t been told the process of how to get to the UK,” said Griffiths.

Some have been interviewed by Home Office officials and then told nothing. Others have provided proof of family in the UK but to no avail. Rumours abound the government has decided to stop accepting child refugees altogether. Asked on Friday what was going on, the Home Office eventually issued a statement indicating transfers from Europe would continue.

Such confusion has meant some children have abandoned the official French reception centres to head north, where they will risk their lives trying to sneak into Britain. For now, both Hassan and Jamil are in secure accommodation – Hassan said his sleep on Tuesday was the best he has ever had. Safe Passage, using a team of formidable French lawyers, has already started putting together their asylum claims.

When talk turns to a fresh start in England, Hassan’s eyes widen. “I want to live with my sister, go to school and then I would love a job,” he said. Jamil wants to save lives. “I want to be educated and excel. After that I want to be a doctor and save people, everyone that I can.”