It's probably just me, but I can't help but feel that we are all missing an important point here. All this discussion of the environment and public transport links is ignoring what seems to be the key reason for the charge - to pay for the third runway and sixth terminal.
The new pricing regime would be introduced if BAA is given permission to expand Heathrow by building a sixth terminal and a third runway.
According to documents seen by the Standard, a new charging regime would help pay for the cost of the expansion, raising up to £137 million a year.
Forget about encouraging people onto public transport (where it exists) and out of their cars, the real point here is that if we want LHR to be a less congested airport (extra runway and terminal) then we have to pay for the privilege. In fact, there is a case that this is a better way of doing it. Instead of just slapping a £20 'airport improvement tax' on every passenger, as many operators/governments have done, BAA are suggesting an arguably rather more eco-sound charge and one that can be avoided provided one is able to use public transport or just leave the car at the airport.