Click to enlarge LONDON is turning inside out. That, anyway, is roughly the argument of a couple ofpieces we have published recently. Just as affluent young professionals seem to be staying in the inner-city longer, turning places such as Dalston (in Hackney) and Peckham (in Southwark) into hipster enclaves, so too are the outer suburbs getting poorer, as people who cannot afford inner-London rents are pushed further out. Anyway, I come back to the topic because since publishing those pieces, Neal Hudson, an analyst at Savills, a big estate agent, sent me the quite fascinating map above. He has calculated a weighted overall NS-Sec figure—the measure of socio-economic class used by the the Office for National Statistics—for London's super output areas in 2001 and 2011. He has then mapped the change. In red areas, the demographic profile of the area has gone upmarket. In blue ones, it has gone downmarket. What's striking about this is how much gentrification is concentrated on just a few areas, typically where there is also a lot of house building—look at the bright red spot over Old Ford, near the Olympic Park, for example. Wander along the canals there and you will see tens of snazzy new apartment buildings and bars, where once there were just knackers yards and abandoned warehouses. The area around Canary Wharf and Spitalfields on the edge of the City is just as marked.

By contrast, the places that have gone downmarket are in Metroland—the 1920s and 1930s railway suburbs stretching west of Acton and Willesden or around Ilford. These are the middle-class suburbs where commuters move when they have children. But of late, house prices in those parts of suburban London have stagnated, even as inner-London ones have soared ahead. In recent years, the outflow of people to the Home Counties has not been matched by the inflow from inner-London, and so population increases have been sustained by immigration and births.

The interesting question is how far this inversion can go. House prices are a significant brake on gentrification in places such as Hackney. Around 40% of properties are still social housing, and so not open to yuppies. Of what's left, the affluent professionals are competing for housing with immigrants, who tend to earn less, but are also more willing to squeeze four or five into a room to cut costs. And eventually, the amount of convenient derelict land on which to build more "luxury developments" without knocking existing stuff down will run out.

What then? In some places, borough councils may be tempted to leverage high property prices to generate cash to redevelop their more run-down parts—turning over their social housing stock to private developers. That, roughly, is what is happening in Elephant and Castle, where the dilapidated 1970s Heygate Estate is being rebuilt as flats to house affluent professionals. Though some of the Heygate's original residents will eventually be able to move back to some of the new flats, most will probably end up settling further out.

That however smacks just a little of social cleansing. At the moment, complaints about gentrification in London tends to be limited to carping about the silliness of hipster bars, or the cost of a burger in Brixton village. But if the future involves the redevelopment of London's long-protected social housing, then the politics of gentrification in London could eventually become quite tetchy.