The extra charged to South Londoners is accentuated by the much greater number of stations which have been placed within Zone 6.
We all pay the same £276 pa GLA precept, but even allowing for the cap, if you make two peak journeys a week from Zone 6 south of the river, you generally pay an extra £235 a year compared with coming from the north. (Unless you're over 60, in which case you pay £8 for each peak hour trip south of the river, and nothing at all north of it!)
Sadiq Khan, of course, lives in the only area south of the river where the Tube has a strong presence.