Call it shameful, call it cruel. The UK now has an effective refugee ban of its very own, targeting the most vulnerable of the vulnerable: unaccompanied children. In the House of Lords yesterday, the minister for immigration, Robert Goodwill, announced the abandonment of the Dubs amendment to the Immigration Act. This was passed last May, after being designed by the peer and refugee Alf Dubs, who fled Nazi-occupied Czechoslovakia as a child, one of thousands rescued in the Kindertransport effort.

Lord Dubs and his supporters had suggested the UK could potentially help 3,000 of the most vulnerable children in Europe - there are estimated to be 90,000 unaccompanied migrant children across the continent as a whole, including thousands who wait in the camps of Greece and Italy, described by Unicef as “alone and extremely vulnerable”. In itself, 3,000 was a modest and achievable number. But now, it emerges, we will be taking only 350 – including 200 who have already come over from the refugee camp in Calais – and we will then slam shut the door.

I worked with the organisation Safe Passage, and volunteer for the charity Help Refugees, and I’m not surprised our government has dodged its responsibility to lone refugee children – it’s been attempting to do this since the beginning. From May, when the amendment passed, until October, when the eviction of the camp in Calais commenced, our government took no action to safeguard children or fast-track their transfer to the UK.

It was only after the fires in the Calais camp, the mayhem that ensued, and its eventual demolition, that children were sent to accommodation centres across France to be interviewed by the UK Home Office. I visited 14 of these centres and found children with one goal – safe arrival in the UK. They were totally distressed by the lack of information they had received. In some centres the mental health of children was visibly deteriorating: they were self-harming and not eating, running away from state protection and back on to the road.

Children who had been relocated to these centres were told they would be given a fair opportunity to make their case for transfer to the UK and have their “best interests” assessed. But when the Home Office began to conduct interviews, the goal posts were moved. The Dubs amendment stated that “the best interests of children” would be foremost in decisions made about their transfer. Instead, in a move criticised by the independent anti-slavery commissioner, the government didn’t consider an eligibility framework centred on “best interest” – one that considered trauma, mental health, risk of abuse or of trafficking.

It decided to discriminate specifically on the basis of age and nationality, only considering refugees under 12, or Syrian and Sudanese refugees under 15 – completely disregarding the needs of Afghan teenagers fleeing the Taliban, Eritrean boys fleeing conscription, and 16- and 17-year-old refugees too young to legally drink alcohol or vote, but apparently old enough to be considered not especially vulnerable. This decision by the Home Office ruled out the majority of those unaccompanied refugee children who had been evicted from Calais.

The immigration minister gave a nod to those left behind in France, stating that “all children not transferred to the UK are in the care of the French authorities”. Except they are not. For the past few weeks I have been back in Calais, helping with night patrols, driving the streets looking for children who are hiding from the authorities under bridges and in the woods around town. More and more arrive each day. With volunteers from Help Refugees and Utopia 56, I bring these children hot food, a mug of tea, and a sleeping bag or an extra pair of socks to help them survive the sub-zero temperatures. More than 150 of them are in Calais, according to Utopia 56, which has been registering children.

Everywhere I look in Calais I’m greeted by familiar faces – young boys and girls I knew from the demolished camp who have returned here. They are despondent and broken. Riot police patrol the area, seeking out children in the side streets and sleeping in bushes. They wait outside the train station in the centre of town to trap returnees. They destroy the shelters that children construct in the woods, take their sleeping bags and fire tear-gas into hiding places.

Utopia 56 estimates over 80% of the children they have seen return to Calais are originally from the Horn of Africa. It is the Eritrean children our government has especially deceived. Last March a delegation of UK officials met the Eritrean government with the intention of coming to an agreement on reducing migration. They offered aid money in return for a promised softening of human rights abuses – this softening never materialised. As a result of new guidance the Home Office put out in response to this agreement, the percentage of successful asylum claims by Eritreans dropped. The Home Office now had the grounds to refuse to consider lone Eritrean children from Calais. And they’re back here, climbing on to trucks, risking their lives to reach the UK by “illegal” means.

Some of them will be successful, but not all. A 16-year-old Eritrean boy called Dawit phoned me after reaching the UK in the back of a refrigerated truck. His travel companion had to be taken to hospital with hypothermia, after the truck was stopped by the British police. Boys show me rips in their clothing and lacerations and bruises they’ve received in their attempts. And then there are those who don’t make it. Last week it was John Sina, a 20-year-old Ethiopian boy, barely out of his teenage years, who was hit by several trucks on the motorway, and killed. Last July a 19-year-old Eritrean called Samarwit was killed in a hit-and-run; in September a 14-year-old Afghan, Raheemullah Oryakhel, fell off a lorry and was struck by a car; and on Christmas Eve a 17-year-old Congolese boy fell from the undercarriage of a truck as it boarded a ferry in Dunkirk, and was crushed.

Who do children in Calais now turn to? They barely trust the UK charities that supported the Dubs amendment. The charities put their faith in the rule of law, expecting that an agreement made in parliament would hold true. But the government’s failure has created a vacuum that will be filled by criminal people-smugglers, the only resort many of these children now feel they have.

The government is treating these children like an immigration statistic to be reduced. If the government is unwilling to act in the best interests of these children, then it is responsible when a child turns to a smuggler, goes missing, or is hit by a truck.

We, the British people, have the willpower, and the public support to tackle this issue, yet Theresa May has chosen not to. Our government has utterly failed these children.