HALF an hour before the interview for this article, Gulwali Passarlay was rung by his brother, Hazrat. “He asked me, ‘What happened last night? What happened? You were screaming in your sleep. You woke me up.’

“I don’t know,” says Gulwali. “Even now, I sometimes wake up screaming.” Sometimes, he adds, it happens after he reads yet another news story about migrants drowning at sea.

Gulwali, now 21, has, with the journalist and author Nadene Ghouri, crafted a remarkably vivid memoir, The Lightless Sky, in which he details his dogged, uncertain, harrowing flight from his native Afghanistan across Europe. His journey took him from his affluent Pashtun family to Pakistan, Iran, Turkey and Bulgaria. He survived spells in squalid, overcrowded prisons and detention centres; he survived an appalling journey across the Mediterranean (even if he was one of the fortunate ones on deck, in the open air – the ship’s captain had locked dozens of men below in the hull). He survived a month in the Jungle, the migrant camp at Calais. All of this, and much, much else besides.

What makes Gulwali’s story even more remarkable is that he was only 12 when it began, during the long aftermath of 9/11, with US forces having toppled the Taliban and swarming over Afghanistan in search of bin Laden. One day, when he was not at home, five of his relatives, including his father, a doctor, and his beloved grandfather, were killed in a firefight with troops who suspected that weapons used in a deadly assault on a base had been stored in the family home.

His family had been Taliban sympathisers (Gulwali’s uncle Lala had been a prominent regional figure in the organisation). Now Taliban representatives wanted Gulwali and Hazrat to martyr themselves to avenge their father's death and help expel the “invaders”; their widowed mother, understandably, wanted her sons to be somewhere else, far away. The family paid $8,000 in order to have Gulwali and Hazrat taken “to safety. To Europe.” But the two boys were soon separated from each other; each continued on his own, with no way of knowing whether his brother was alive or dead.

The Lightless Sky leaves you fearing for Gulwali’s safety and admiring his utterly tenacious resolve to reach Britain against overwhelming odds; but at the same time it is also a fearsome reminder of the experiences being endured, even as you read this, by numberless, anonymous migrants. Not for nothing has it all been described as Europe’s biggest humanitarian crisis since the Second World War.

I tell Gulwali that I admired his perseverance in the book. “Thank you,” he responds, politely. “But the thing is, there are millions of people like me who are going through the same struggle and enduring the same pain and suffering, even if they don’t have a platform to have a voice. I hope my story will be a kind of representation of those many millions of stories. It is not unique in any way. People go through the same, if not worse.” Indeed, he dedicates the book not just to his mother but to the "60 million refugees and internally displaced people … risking their lives to reach safety.”

Here and there in Gulwali’s riveting account there are traces of human kindness, people who helped him out. But it is hard not to be revolted by the cynical opportunism of many of those involved in migrant smuggling. He writes about his small band of migrant friends being “tricked by the smiling liars in leather jackets and Land Cruisers.” One chapter set in eastern Turkey has 15 migrants living in a chicken coop, filthy and cramped, under the eye of a bald, scruffy alcoholic in a dressing-gown. The toilet was the least of the horrors.

“I suppose I saw both sides of humanity [during his year-long journey],” he says. “But the majority of people are nice, they are kind.”

Eventually, Gulwali escaped from Calais by hiding on board a refrigerated lorry. He made it to Dover but was caught. British officialdom stubbornly refused to believe that he was only 13. It asserted that he was a few years older.

Gulwali’s early time in this country did not go well. He felt lonely, frustrated, depressed, alienated, and at one point tried to kill himself. Later, in Manchester, even as his prospects were improving, and he had been re-united with Hazrat, he tried again. He writes that he couldn’t cope with the fact that his life was improving. “At night I still woke in sweats and tears as the nightmares gripped my soul.”

He initially did not want to include the suicide attempts in the book but was persuaded to do so by his co-author. “I wanted, in the end, to show that the system here makes you so unwelcome that you want to take your life," is how he puts it.

Gulwali’s life since those unhappy days of 2007-08 has improved more than he could have dared hope. Hazrat became his legal guardian and the brothers briefly shared a rented house in Bolton. When Hazrat returned home, Gulwali was put in the care of a foster family. They helped turn his fortunes around. He flung himself into school life, and did well in his GCSEs. In September 2011 he began attending Bolton Sixth Form College to do A-levels in politics, economics, philosophy and Urdu. He became a political activist, speaking up for children in care, mainly refugees. He was granted asylum, won a place at Manchester University, and in 2012 he helped carry the Olympic torch through Burnley as it made its way to London. It was, he writes, “a life-changing moment” and “one of the most special things I would ever do.”

Today, Gulwali is in his third year of a politics degree at Manchester. He does much youth activism, campaigning and community work, and describes himself as an aspiring politician. His aim, he says, is simple: “I want to help people less fortunate than myself.”

He phones his mother in Afghanistan regularly. “I tell her about the things I am up to,” he says, “but I talk about how she saved me but in doing so she lost me as well. It’s hard, it’s hard.” A younger sister back home recently passed away.

Gulwali is grateful for all that Britain has done for him and for giving him so many chances. He talks admiringly of meeting Channel 4’s Jon Snow and comedian Russell Howard. “My ambition is hopefully to go back [to Afghanistan] one day to ensure that children like myself do not have to leave their family, their country and their home, and don’t have to risk their lives,” he says. “Not yet, though: it is very risky. But one day – I hope.

“I miss it very much, though. There is not one day I don’t think about my country, my family, my home, my friends.” He remains passionate, as you would expect, about the migrants who are following in his wake. All they want, he insists, more than once, is to be treated as humans, with dignity. He recently headed a big march in London to welcome refugees; he has even gone back to Calais to visit the refugees who are marooned there. He believes we are failing refugee children.

In a note at the end of The Lightless Sky, his co-author Nadene Ghouri observes that at least 2,000 men, women and children are known to have drowned in the Mediterranean this year alone.

A few days before the interview with Gulwali, a wooden boat carrying dozens of migrants from Turkey to Europe capsized off Lesbos after colliding with a Greek coastguard vessel during a migrant rescue operation. At least seven people died, three of them children. Last Sunday, at least three other migrants drowned off Lesbos. “These deaths,” Gulwali says, resignedly, “are just the ones we know about.” Years ago, Gulwali could have drowned, too. But his luck held.

The Lightless Sky: An Afghan Refugee Boy’s Journey of Escape to a New Life in Britain (Atlantic Books, £18.99). Gulwali will be at the Edinburgh Independent Radical Book Fair, 30-38 Dalmeny Street, Edinburgh, on Sunday November 1 at 2.45pm.