I am surprised not to see a reference to
http://www.tfl.gov.uk/tfl/roadusers/...ternextension/
default.aspx

I find it interesting that the census questions do not distinguish
drivers and non-drivers. They also redundantly ask for a respondent's
post code and whether the respondent lives in the western extension
zone.

It looks as if the result will be to modify the implementation.
I go for that. Although I think the western extension was a bad idea, I
think scrapping the hardware would be unconscionable.
--
Walter Briscoe