I don't think anybody seriously thinks Mode S is anything to do with airspace charging involving the tracking of transponding aircraft.
The radar coverage doesn't exist and would cost countless millions to implement, be of no benefit to the real players in aviation (the airlines) - just to collect a pittance from the bulk of GA pilots who fly VFR at low level.
En-route charges for VFR will come and almost certainly will be a flat rate charge (quarterly or annual) on every aircraft known to the CAA to be UK based.
What Mode S will do (assuming people don't contravene the coming regulations and leave the transponder switched on) is that it will make it easier to identify aircraft infringing some airspace. But its primary purpose is for more efficient air traffic control, which is there mostly for the airlines.
But this stuff has been done to death already here and elsewhere...
In the end, the plane spotters will ALWAYS get you, and your details WILL appear on some spotter website
