I’ve interviewed Gary Stevenson three times. First in 2020 about global finance being screwed with a capital “S”; again in 2022 about the cost of living crisis; and then last year when he published The Trading Game, his compelling memoir about life as a trader at Citibank. Now I’m meeting him for the first time in the flesh, ahead of the book’s appearance in paperback, and we’re talking about yet another crisis.

“Have you seen the news?” is the first thing he asks, presenting it like a challenge even before he says “hello”. I rack my brain distressingly slowly, like a librarian using a card index for the very first time, thinking: which bit of the news? LA is on fire; Gaza is on fire; Ukraine is on fire; a bunch of Teslas are on fire. Seriously, we’ve all seen a lot of news.

“Traders are about to bring down the government,” he says.

Oh, that news. “They’re selling the bonds,” Stevenson reminds me. “Not with the same speed as with Truss, but they’re selling them. Interest rates are at 4.9% this morning. In my opinion, and the opinion of most unbiased economists, the government can’t afford to fund itself at 4.9%.”

There are fundamentals here that I’m embarrassed to admit I don’t really get. Part of the appeal of Stevenson – who, despite being 38, reminds me of a young Mike Skinner, with his hoodie, trainers, buzz cut and intensity leavened with insistent humour – is that he doesn’t mind. He doesn’t really think anybody gets it except him. “Nobody on the whole fucking left understands what’s happening on the financial markets except me,” he says. “I’m on all these left-wing WhatsApp groups, I’ve had spads messaging me, saying: ‘What can we say?’ Because I’m the only guy that knows. And I’ve been screaming, for months: ‘Watch the bond yields, watch the bond yields, watch the bond yields.’”

But why wouldn’t the markets just give a rightish-centre-left, completely unradical, relatively new government a chance? “Traders individually are smart people, but the market itself is a little bit of a wild beast. But the thing is, the traders are probably right. If you look at the UK government, it’s not on a sustainable financial path. There’s been no sustained growth in this country for a long time. The government’s stripped to its bones. The middle class is dying. Where’s the growth going to come from? What is the actual plan here?”

Market movements, market trends: these are all just a disembodied way of saying “rich people”. And Stevenson knows a lot about the rich. After all, he’s one of them, thanks to his years at Citibank and an even more profitable second act trading for his own account. Since 2020 he’s been running a YouTube channel, GarysEconomics, explaining to his 620,000 subscribers how the rich have grabbed everyone else’s money.

“The rich have got a choice,” he says. “They can lend the money to the government or they can buy the assets. I know what I’m doing.”

“OK, what’s that?” I ask, trepidatiously, knowing the answer.

“I’m buying the assets. Stocks, gold, commodities, property, everything. The rich have got a lot of money, they can buy everything. The government has got to compete with that. They can’t. They’re trying to play chess with no pieces.”

Stevenson’s is an incredible story. He was born in Ilford in east London: “I grew up in a tiny little bedroom. I had one drawer under my bed with everything I owned in it. I’m not good at owning shit, I’m not good at decorating shit, I’m good at talking about economics.” He is expelled from grammar school, gets into LSE anyway, wins an internship at Citibank on a card game, gets a job, becomes the most profitable trader at the bank in 2011, is a multimillionaire by his mid-20s, has a mighty clash with the bank and then a breakdown but walks away the winner anyway. None of that is a spoiler for his book, I don’t think, because the real drama is what’s happening to the economy.

“I pitched this book to Penguin in 2022,” he says, “and said to them, ‘If you think the economy is bad now, wait until this book comes out. Politics and economics are increasingly gonna be everything people care about, because this gets worse. The world’s falling apart, and it’s not gonna get better.’”

Six months after The Trading Game was published, former colleagues lined up to tell the Mail and the Financial Times it was nonsense. He had never been the best trader at Citibank, they said, and it wasn’t even possible for him to know either way. And besides, his mentor and colleague Billy (a pseudonym) was. “It’s such a trader response,” he says, “that they’ve zoned in on this: ‘He wasn’t the best trader.’ You write a book, basically saying the global economy’s going to collapse. And they’re like, ‘He’s not the best trader.’ It’s the only thing they can say: ‘I made more money than you.’”

He stands by his claims, “but it can make a person go mad, to be called a liar, again and again”.

While living in Japan with his girlfriend, called Wizard in the book, Stevenson had a breakdown, which was a long time in the making. Before he’d left for Tokyo, he’d fallen out and stopped living with a family friend, who was younger than him. “When we had this big split, he called me and said, ‘You fucking need me.’ And it’s right, in a way; I looked after him like a father, and he kept me human. When he goes, life is nothing but the numbers.”

He was already embroiled in a battle with his employers, who didn’t want to pay his astronomical bonuses unless he stayed. This is apparently very common in the City, and maybe doesn’t come up in conversation much because people making huge bonuses never want to leave.

He describes one meeting he had with HR, all of which he spent staring at a desk-photo of the HR manager’s family. He does an impression of himself, staring. It is funny, and it is genuinely unsettling. “I didn’t keep it together, but I still got the money, didn’t I? There was a wonderful reclamation of humanity through defeating these guys by being mad, rather than by playing their game. I was born and raised poor in London. I went to grammar school, got judged for being poor. I got expelled from school, I went to LSE, I went to Citibank: everybody was always richer than me. I had to study for my exams sat on my bedroom floor. There’s this thing for young people: work harder, be better. And I was like, ‘No, I’m just going to be an idiot.’”

He came out of it depressed, weighing eight stone, isolated, behaving erratically. “It’s about a total numbness, feeling nothing. You don’t care if you haven’t eaten for five days, you don’t care if you haven’t brushed your teeth – it’s a total separation from the world. If you can enable people who’ve never experienced depression to in some way feel it, that would be a service. I don’t want people to sit listening to Prince William on a podcast – I want you to be there. I want you to be a little bit confused, because I was confused. I was a multimillionaire in my mid-20s, I had a beautiful girlfriend, and I was unhappy.”

After doing an MPhil in economics in Oxford, he came back to London, bouncing between friends’ sofas before moving back into his flat in Limehouse – a stone’s throw from Citibank’s offices in Canary Wharf and bought with his ginormous bonus. It was ground zero for the irrationality of his experience, “to devote your youth to getting good at something, and the culmination of that thing being simultaneously realising that the global economy is gonna collapse and being paid £2m. ‘You are the best at this thing, you are totally right, the global economy’s going to collapse. Here’s £2m – go do it again.’”

As for why he still lives there two years later: “These skyscrapers [in Canary Wharf], they went up when me and my school friends were seven or eight. We could see them in the distance, on the horizon, from Ilford. We felt like it belonged to us. For me, Canary Wharf is a shitty, plastic place but I fucking killed that shitty, plastic place.”

Stevenson still makes a lot of money trading, which he does “to demonstrate to myself that I’m not insane. A lot of people can say pessimistic things, but not a lot of them can make hundreds of thousands of pounds every year on financial markets. I don’t just say these things; I bet on them. And I make money every year. You can’t do that if you’re not right. If you made every economist who chats shit on the media bet their own personal money on what they’re saying, there’d be a lot less bullshit on the news.”

But his sights are all on politics. “Andrew Tate is seeing the same thing I’m seeing. Politics is dying,” he says. “The far right are settling now. They know what their plan is: anti-immigration is the big idea, Muslims are the bad guys, tariffs. There is a battle of ideas in society, but there is a battle of ideas on the left. I’m putting my pitch forward – I’m going to build something about inequality, taxing the rich, and I’m going to build it on YouTube. These are very ambitious plans, but what else am I supposed to do?”

Wait a second: does he actually want to be prime minister? “This is quite a simple idea: if you don’t do something about inequality, it will get worse, and living standards will continue to fall. That idea is pretty simple. It doesn’t need to be all on my shoulders. I’m trying to set a fire under the people. I’m trying to get them pumped on it.” It may be the first thing he’s said that’s not quite an answer.

• The Trading Game by Gary Stevenson will be published by Penguin in paperback (£10.99) on 30 January