So, what we now need to know is would the level of NO2 drop below
the legal limit if Hackney Cab drivers all went over to a hybrid vehicle.

The second important piece of information is which vehicles and
drivers have now given up coming into central London. Anti-motor car
politicians always assume it's joy-riding motor car enthusiasts making
unnecessary journeys who have been repelled, but what if it's tradesmen
providing essential services who now refuse to serve inner London?

A third detail will not in any circumstances be made public: how do
the new levels of NO2 compare with those prior to London having a
Mayor?