Based on the environment in which he was raised, he explores the anger, resentment and the sense of exclusion of the underclass, trying to explain what led voters to back Brexit and right-wing nationalism and populism.

“Often in communities like mine, or any community characterized as poor, the tropes associated with it are all about behaviors,” Mr. McGarvey said in a recent interview in a house in Pollok, the housing estate where he was raised. “I wanted to fill in the gaps and say, ‘Here’s what I think drives attitudes, behaviors and circumstances.’”

As inequality widens, he argues, assumptions about people on the other side of the divide become ever more entrenched. People have become so tribal that “politicians have little choice but to supply our demand for illusory quick fixes, oversimplified sound bites, scapegoats,” he said. “The biggest feature of the tribalism that comes to characterize our culture is the belief in the legitimacy of our resentments.”

In “Poverty Safari,” he describes how, in the violent milieu in which they are raised, children of the underclass become skillful emotional manipulators, intuiting their abusers’ needs and triggers. The eldest of five, Mr. McGarvey attributes his unusually high sense of self-awareness and keen observation to his “hyper-vigilance” as a child, living in fear of his mother, who herself was a victim of abuse and sexual assault.

He tries to make the pressures of deprivation relatable to the financially secure, bridging the gap between upper- and working-class realities: the chronic stress that spills into bingeing on booze and junk food; and the insidious belief that you are not smart enough or will never amount to anything, feelings that can manifest as aggressiveness.

He criticizes the left for being too wound up in righteous anger and obsessed with ideology, instead of trying to make practical differences to those who need help. The “poverty industry” run by the middle classes, he said, misunderstands deprivation because they are not part of it, however well-intentioned they are.

“This experiential reality of poverty has to inform how we deal with people,” he said. “We have to account for how people experience this society and the barriers.” The failure of the left to discuss issues like immigration, he says, has created a vacuum that is being filled by the far right.