To this day, Jeremiah Emmanuel remembers the first time he caught the 345 bus from Brixton, when he was eight years old. “The last stop said South Kensington – I had never heard of this area before. So I’m looking out the window, and it looks really different. By the time you got to Chelsea, the floor looked the same colour as the day it was paved,” he says, now 21. “I felt like there were so many communities who were so close together and so far away living on parallel lines. Why is there so much inequality in the country?”

The shifts seen out the window of the 345 embody the question at the heart of Emmanuel’s debut book, Dreaming in a Nightmare: Finding a Way Forward in a World That’s Holding You Back. What separated the world at the other end of that bus trip from where it began, next to his favourite haunts: Creams, a dessert cafe where he and his friends would congregate and eat Oreo waffles after, he says, “youth services in Lambeth got decimated”; or the Brixton McDonald’s, also known as “Brikky McD’s”.

“For us, it was safe because we had nowhere else to go,” he says, of the latter. “But there was drug misuse in the toilets, people were selling drugs outside, you had fights inside, there was no supervision from adults. For me, it was just the norm. I would hang out in McDonald’s for hours, run over to Lambeth town hall to do my youth politics, then run back to be with my friends again.”

When we meet, we’re near his new home in Vauxhall, just north of Brixton. He proudly holds his book, with his BEM (British Empire Medal), which he received for his services to young people in 2017, on the table in front of him. These are just two of a striking roll call of achievements; a member of the UK Youth Parliament at 11, former deputy young mayor of Lambeth at 13, a former army cadet. He now works with the Gates Foundation and describes himself as a “youth activist and social entrepreneur”.

On the face of it, all this can be seen as a far cry from the trauma in his early life that he describes in the book: being frequently homeless with his mother and siblings until he was seven; being aggressively stopped and searched by police when he was 15 – in the same week as visiting Downing Street to collect an award for his community work; and performing first aid at a house party on a boy who had been stabbed.

Your definition of success isn’t going to be the same as someone who’s gone to Eton where they’ve been prepared to be future prime ministers

“A major way that I got over my trauma was by forgetting,” he says. “My father passing, being homeless, the brief stint in the care system, when my mum got ill – I lost my memory. It was all just impressions … The writing process brought it back.”

The title, Dreaming in a Nightmare, he is keen to clarify, relates not to Brixton specifically, but to any environment that actively disempowers its citizens. Billed as a memoir, he also calls it a toolkit for empowering young people, to lay out the methods he has used to find success. Like persistence and self-belief, both seen in the email (printed in the book to be used as a practical template) that he sent to the chief executive of Rolls-Royce, aged 17, offering to help the company connect with young people: “Last year, I founded the BBC Radio 1/1Xtra Youth Council … I think Rolls-Royce would benefit from the advice of a similar group.” Rolls-Royce then hired Emmanuel to help it attract more job applicants from young people.

“You can only see what is in front of you,” he says now. “So your definition of success isn’t going to be the same as someone who’s gone to Eton where they’ve been prepared to be a future prime minister or the CEO of Fortune 500 companies. We need to see it.”

While the memoir of a 21-year-old must operate differently from a memoir that comes with more lived experience, reading Dreaming in a Nightmare gives the sense of how bearing the brunt of austerity Britain ages a person. The impact of the 2008-09 recession, the student debt that he was once scared of, the need to work for a charity to plug the gaps of government – all reflect the prospects and challenges facing Gen-Z. Emmanuel includes interviews with his peers to bolster his points, such as Kayla, a close friend and unofficial news broadcaster who will call if there is bad news; or Nathan John-Baptiste, AKA “the Wolf of Walthamstow”, who made more than £25,000 selling snacks from his school toilets back in 2017. Emmanuelwas lacking in his own entrepreneurial approach as a one-time muffin magnate at school. As he humbly acknowledges: “The first business lesson I learned was an important one: never eat your own product.”

Dreaming in a Nightmare was his first foray into professional writing, after the musician Stormzy met Emmanuel through his youth work, and forwarded the manuscript to his Penguin imprint Merky Books. Nine drafts and 12 months later, Emmanuel had a book, written while listening to the soundtrack from his childhood: gospel singers Kirk Franklin and Donnie McClurkin, Afrobeat pioneer Fela Kuti and Nigerian rapper Burna Boy, as a way to bring him closer to his ancestry.