Comment by noneeeed
It's a big issue there but it's very localised to that specific area (which is itself in the bottom 25% of areas in the UK). They are like having a whole load of idling lorries sat near your house all at the same time, normally for several days at a time. And all of that is on top of the general level of pollution from being in the centre of London. I'm going from a documentary and a couple of article from a few years ago, which I should try and find.
Hopefully with all the work on both improving the fuel used, and providing grid hookups so they can turn their engines off, that will have made a big difference. Hopefully the effects of the congestion charges have made a big difference too. A lot of the kids featured in the documentary had a really crap life because of it all.