Expats find a perverse satisfaction in checking daily American embassy air quality readings; the higher the pollution score, the more they feel intrepid, a breed apart. But especially foreigners with kids cited the air as a leading reason why they were planning to leave.

And the architecture! Never was any city more captivated by the rectangle. As you take off from Beijing airport, clumps of residential developments rise relentlessly into the distance, each cluster often 60 or so high-rises apiece, each high-rise 50 or so stories tall — seeming to reproduce SimCity-style as you watch. They are all drab, they are all the same, they are all hideous. (A student asked after my event whether perhaps I didn't care for Beijing's architecture merely because it was "unfamiliar". I looked at him in astonishment. "Unfamiliar!" I exclaimed. This stuff is all over the world!" And an assault of Bauhaus is hardly Chinese.) Put up in the engineering equivalent of 15 minutes, none of these buildings is made to last — but when I asked my winsome Han tour guide what would happen when they collapsed, she said with cheerful gusto, "We'll build them again!"

For a Londoner, the difference between a city of eight million people and one of more like 22 million is staggering (and it tells you something about the limits of the seemingly all-knowing, all-powerful Communist Party that the authorities have no idea how many people live in the capital). The city's numbing extent, its smog, and the wearing anonymity of its dreary housing recalled eco-disaster films of my youth like Soylent Green.

Most Chinese would have little time for my aesthetic reservations. Those identikit apartment blocks have indoor plumbing, electricity and running water, thereby raising the living standards of millions of former peasants. The sheer logistical feat of having housed and built infrastructure for a population of such inconceivable size is humbling. In the UK, HS2 is meant to be finished in 2033. The Chinese would knock together that rail line in a weekend.