Over the past few days, as condemnation has rained down on Donald Trump for ripping toddlers from the arms of their immigrant parents, my thoughts have turned to a small, scared boy far closer to home. Five thousand miles separate the Texas-Mexico border from Folkestone in Kent, where Bashir Khan Ahmadzai sleeps in a child-sized bed underneath a calendar that is two years out of date. However dire, his situation will not draw the TV anchors or be commemorated by a Getty photographer. Yet the more I turn over his story, the more troubled I am not just for him, but for what it says about our politics and our media.

To scream at the barbarian in the White House, to denounce Italy’s thuggish deputy prime minister Matteo Salvini, to shudder at Hungary’s leader, Viktor Orbán: such acts come easily to decent politicians and pundits. And so they should, because each of these men normalises a racist brutalism. Yet to stop there is merely to play liberal pantomime. The harder, but just as essential, task is to look away from the TV screens and headlines and spot signs of the same casual racist brutalism at home, in our political system, in a case such as that of Ahmadzai.

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The term everyone uses for Ahmadzai is “vulnerable”. His friends say it. People who work with him say it. Even tough-minded judges use it, again and again. And when you meet him, as I did last week, you see why. He is skin and bones and wide brown eyes, and he wears on each ear a hearing aid that fizzes static. The authorities have him down as 21 years old, but that seems a stretch. His housemate Khalil Niazi says: “He is like a child. I make sure he’s OK.”

Ahmadzai certainly came to Britain as a child, nearly six years ago, from provincial Afghanistan. His father, a policeman, had just been murdered by the Taliban. Then they came looking for him, he recalls, and his mother sent him away. On arrival in Britain, the boy applied for asylum but somehow it was recorded that he had grandparents in Kabul who could look after him. Ahmadzai denies ever saying such a thing, while Niazi reckons the interpreter just didn’t understand him: “My other Afghan friends – even they can’t catch what he’s saying.” Court documents I have seen agree he has “complex speech, language and communication difficulties”.

Still, that point about having relatives in Kabul followed him through the system and helped to ensure he was given not asylum but temporary leave to remain here while a minor. Now he’s apparently an adult, and has to report regularly at Lunar House immigration centre in Croydon, on the outskirts of London.

Last month, Ahmadzai went in to sign on as normal. It should have taken moments, but the official asked him to stay behind for a while, which turned into hours, which turned into him being transported to Brook House – the low-rise block near Gatwick airport where the government often warehouses Afghans and others before forcing them on to planes out of the country.

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He was locked in a small cell: a toilet, a bed, a small window he couldn’t see out of, and a spyhole to allow officials to look in. There was shouting and planes roaring overhead and he had no idea what was going on. But when he told the officers that he wasn’t well, that he had health problems, that he felt weak from fasting for Ramadan, they kept silent. Instead, they told him, rudely, brusquely: “We’re going to deport you.” They said it so often it became almost a chant: “We’re going to deport you, we’re going to deport you, we’re going to deport you.” Afghanistan, according to the Home Office’s own guidance, is “the second-least peaceful country in the world after Syria”. In each of the past five years well over 10,000 civilians have died or been injured by roadside bombs, in suicide attacks, or from other forms of armed violence. The British government warns us against travelling there, yet it was happy to dump there a youth described by the courts as “dependent on others for his wellbeing and general welfare”.

I ask what Ahmadzai would have done in Kabul. Even in Folkestone, he says, he can’t leave the house at night because gangs of boys beat him up. Then he imagines life in a country as broken as Afghanistan 17 years after a war begun by Britain and America and their other allies. His family is in the north-eastern province of Baghlan, where the Taliban is constantly taking towns – and he doesn’t even have their address.

His friend Niazi translates this, then tells me in low, even English that he knows Ahmadzai can’t follow: “I think in Kabul he would die.” Knowing what we do about Afghanistan, this doesn’t sound hyperbolic. Yet our government was willing to take that risk with a highly vulnerable young man. The Home Office didn’t respond to my questions on his case but said: “We take responsibilities of health and welfare very seriously and we are working closely with partners to ensure Mr Ahmadzai is receiving the support he needs.” Yet of those “partners”, I understand that Kent county council did not know he was going to be detained, and his social worker wrote to plead for his safety. (The council did not issue an official response.)

Ahmadzai did not sleep at Brook House. He would ring his friend and carer Niazi again and again: what was going to happen, what was he going to do? “He kept saying to me, ‘I’m scared, I’m scared.’” Then after four days, as suddenly as he’d been taken, he was released.

However dramatic his story, it is worryingly common for Afghans. The immigration barrister Colin Yeo points out that the Home Office habitually detains hundreds of Afghans a year then releases three-quarters of them. It is a form of opportunistic gambling with people’s lives – bring them in, bang them up, then see if you can drag them into a seat on a plane where they will no longer be your problem. And if that doesn’t work, well, you’ve given them one hell of a scare. Just like those border guards do in El Paso.

The British state helped to cause the mess in Afghanistan that forced Ahmadzai to flee – now it is punishing him for escaping it. At Goldsmiths, University of London, Prof Sue Clayton points out that from the early 2000s onwards, the Home Office regularly rounded up Afghans and dragooned them on to “ghost flights” from airport cargo terminals in the middle of the night. The practice only stopped in 2015, thanks to overwhelming protest.

This happened under Tony Blair, Gordon Brown and David Cameron. Theresa May was the home secretary who petitioned for the likes of Ahmadzai to be forced out of Britain. These are not callous extremists but they had no shame about using some of the same tactics and going after some of the same targets, and they did so against a similar media backdrop. When the rightwing US commentator Ann Coulter describes crying infants at the Texas border as “child actors”, she is only doing bigger and bolder what our press and Tory MPs did when they described the child refugees fleeing the Calais migrant camp as being adults in disguise.

An easy comfort resides in shaking your fist at the foreign monster on your plasma screen while ignoring the monstrousness done right here. There is a thin line between justified outrage and hypocrisy – and you cross it when you don’t examine the outrages perpetrated in your name. To believe this era of demeaning and dehumanising others simply because of their country of birth only began with the Brexit vote – that we lurched from 2016 straight into the 1930s – is to commit to flawed history and failed politics. To march against Trump while doing nothing when the far right turns out in their tens of thousands for Tommy Robinson is the kind of self-satisfied blindness that sees threats on distant shores but misses those right under its nose.

Niazi knows about Trump’s new immigration policy. “What’s happening there is horrible; it makes me angry,” he says. “But look at the way the government treats Bashir [Ahmadzai] – they’re not showing him any compassion.” Ahmadzai has been asked to sign in again at Lunar House on Wednesday.

• Aditya Chakrabortty is a Guardian columnist