For McGuirk, the solution is to integrate the informal and formal cities. In the introduction to his book, he argues that, “Accepting the informal city as an unavoidable feature of the urban condition, and not as a city-in-waiting, is the key lesson that this generation of Latin American architecture can offer the world”. In other words, getting rid of slums won’t solve the problem: improving and integrating them might.

In McGuirk’s eyes, architects play a crucial role in this process, sitting somewhere between civic officials and the people of the city: “The job of the architect is to harness government resources; to rehabilitate or retrofit the informal city with some of the advantages of the former city, and to bring the two together.”

The role of the slums is in some ways changing anyway. In Rio, one recent development that could improve quality of life is the favelas’ growing tourist industry. But for McGuirk, this has had an “ambiguous” effect: while it gives slums a sense of permanence, tourism-oriented development diverts funds away from much-needed infrastructure and towards cable cars and guest houses.

In fact, city officials did have more concrete plans to improve the favelas, but these were sidelined during preparations for the World Cup and the 2016 Rio Olympics. McGuirk calls the Brazilian government’s approach to both events a “wasted opportunity”. “I think it’s obscene that when it comes to favela upgrading, only a little bit of money can be found, but when it comes to building white elephant stadiums, billions of dollars can.”

More positive, in his view, is the fact that European migrant workers are moving to the favelas, something that would have been unthinkable even ten years ago. “It does suggest that if Europeans can find value, and homes, in the favela, Brazilian politicians might start to see them differently too.”

This admission, that demographic change can be as revolutionary to slums as new transport networks, mirrors a pattern that runs throughout Radical Cities. As McGuirk says, “It started off as a book about architecture, and became a book about cities.”

The chapter on Bogotá, for example, focuses on the eccentric policies of Antanas Mockus, a philosopher and lecturer who was the city’s mayor in the late 1990s and early 2000s. His campaigns, including cutting licensing hours during December to cut homicides and raising domestic violence awareness among children, have become iconic in the experimental city politics.

“I just thought it was important to share Mockus’ ideas in particular,” McGuirk goes on, “because mayors tend to think they have to build things and cut ribbons, whereas actually, sometimes there's no money to do that. But that doesn't mean that you can't leave an important, intangible legacy. If you can't afford to change the hardware, change the software.”

His emphasis on improving the slums, rather than reinventing them, has attracted its fair share of critics. In a review for Disegno magazine, Owen Hatherley warns that the book is “potentially bad counsel for the future of public housing and public architecture”.

Yet McGuirk thinks this is missing the point. “[Top-down planning] makes sense if you’re building a city from scratch, but the problem with the informal city is that it is already there. These people who say 'you need good planning, you need good architecture’ – well, it's too late, for a billion people across the world.”

His next piece of research will move even further away from architecture, towards design technology. Yet his work in Latin America has left him with unanswered questions: “Radical Cities a very optimistic book, but now, the question on my mind is ‘What have I just documented? Is it the beginning of something, or the end?’”