Shortly before midnight, volunteers with a French refugee charity located six teenage refugees from Eritrea hiding in bushes in a dip at the side of the A216 motorway leading to Calais.

As they distributed tea, food and sleeping bags, a car stopped by the roadside and five plainclothed police officers came out, shining torches in the faces of the boys, the youngest of whom was 14. “Take your food and run,” Sarah Arrom, a volunteer with Utopia56, told them, and they disappeared at speed into the freezing mist.



Trying to help the estimated 200 refugee children sleeping rough around the port has become a fraught and often clandestine operation. Police took the names and addresses of the student volunteers who were trying to give bedding to the children, and told them what they were doing was illegal.



Following the demolition of the vast Calais migrant camp last November, local authorities are taking a hard line with any sign of new settlements, so the children sleep without tents to stay hidden, and do not risk staying two nights in the same place or lighting fires to keep warm. If conditions in the vast camp were highly inappropriate for children, they are now far worse.



“It’s very cold. We have no food, no water, no bed, no toilets. It’s dangerous,” one of the older boys, a 17-year-old from Asmara, Eritrea, said. “We don’t sleep. There is nowhere safe.” As soon as he saw the flash of the police torches he disappeared, familiar with the French police’s generally hostile approach to refugees.



All six boys had been told they might be eligible to come legally to the UK under the Dubs scheme, which was established last year amid a brief surge in political and public concern over the fate of child refugees in Europe. They were housed for two months in a French accommodation centre while their applications were processed. When they found out at the end of last year that they had been rejected, they returned to Calais to sleep rough and attempt to continue their journey, spending every night trying to smuggle themselves into lorries to get to the UK.



“They made promises when the jungle was demolished, and now we are back in this horrible situation. We don’t want to be here,” a 16-year-old said. “We want to be getting an education.”



They were among around 1,000 teenage asylum seekers bussed from the migrant site in November to accommodation centres around France, where they were interviewed by Home Office officials. Only 150 were given permission to travel to Britain under the Dubs legislation. Of the rest, some have decided to stay in France, but those who have relatives in the UK, or speak good English, or whose parents have told them that they should continue to get to the UK, are gradually making their way back to Calais.



Aid workers, from groups such as Help Refugees, who are trying to provide food for the children said the numbers sleeping rough in the wastelands around Calais were increasing every day, most of them from Eritrea, Ethiopia and Sudan. Minors from Afghanistan and Iraq are travelling to other refugee camps along the coast.



The return of the migrant teenagers places charities in a uncomfortable position. They want to avoid encouraging more children to sleep rough, so they no longer distribute tents – but they also see the urgent need to provide food and blankets. They try to inform the adolescents that staying in France may be a better option for them, but few are convinced. In the meantime, volunteers distribute food parcels (and bread when it is donated by people in the town) and take boys to the nearby hospital when they are ill, usually suffering from suspected hypothermia.



Twenty minutes after the police officers had left, the boys emerged again from the undergrowth, and took the sleeping bags. Sarah Arrom, taking a break from law studies in Paris to volunteer, told the teenagers they needed to put the sleeping bag on top of an emergency insulating silver blanket, to protect themselves against the ground frost, but she was doubtful her advice would be followed.

“We’re always asking them – have you got your hat, your gloves, warm clothes on? But they’re children. It’s very dangerous for them to be sleeping out like this.” In the past few weeks she has met several 13- and 14-year-olds from Eritrea, although the majority were a bit older, between 15 and 18.



“If they are really cold we put them in a car for a while, put on some music, let them warm up. With the adrenaline, they don’t realise how cold they are. They talk about Trump and Theresa May, they are educated people, but they are worried for their future,” Arrom said.

Discarded sleeping bags in the undergrowth outside Calais. Photograph: Alecsandra Raluca Dragoi/The Guardian

A mile away, at the end of a cul-de-sac, in a deserted industrial zone on the fringes of the city, around 15 boys were huddled beneath an electricity pylon waiting for Utopia56’s 1am delivery of food supplies, but no sooner had volunteers started pouring tea, than a police van arrived and the boys dropped their sleeping bags, left their food and fled, disappearing within seconds into the dark forest.

A friendly officer from Burgundy said it was his job to protect the children, and claimed that the nightly patrols were designed to ensure they were not in danger, but this explanation prompted some scepticism from the people distributing food, who suggested the state should be helping provide food and shelter.

“I am human. It’s not good to see them sleeping outside when I am going back to my warm home. I have compassion for them, but it is difficult. What is France meant to do? We can’t accept the whole world,” the officer said. He predicted that numbers would increase once the weather got warmer.

In the morning, there were signs that refugees had been sleeping in the forest and the rough, sandy wasteland beyond the factories on the edge of the town. There were trainers, empty milk cartons, sleeping bags, sodden from the damp ground and left lined up behind the scant protection of a few bushes.

Najie, 16, from Sudan, had arrived back from a French accommodation centre three weeks ago, travelling alone. His application to go legally to the UK had also been rejected, so he was again trying to go illegally. He said he was tired, and unable to sleep.

“They walk all night, until they are really exhausted, then they might rest for a while hiding under a bridge. One boy said he slept, standing, propped up against a tree trunk so that the police wouldn’t spot him. They are dirty, exhausted and hungry,” said Vincent de Coninck, who manages the Secours Catholique day centre on the edge of Calais. Around 50 boys were at the centre on Friday, 30 of them asleep on mats on the floor. “Another boy told me he has started burying his food, and a thermos of coffee, so he knows that even if he is chased by the police, there is a safe place he can find his food. It’s horrific – children burying food in France.”

In justification for the decision to curtail the Dubs scheme, the British government has said it wants to avoid creating a “pull factor” that might encourage more parents to send their children across Europe, but De Coninck said it was ridiculous to think that any of these minors or their parents had any knowledge of UK asylum law; most travelled to Calais simply because they were aware that this was a good place to get on lorries traveling to the UK.

“They don’t know anything about the system. I try to tell them they will be better off staying in France, but the smugglers give them false information. The only way to fight against this mafia is to offer a legal way to get to the UK, and yet the British government has just done the exact opposite,” he said. “I can’t decide who I feel more angry with – the French or the British.”