Hi Richard
Assuming you are genuine and not one of the Numpty Anti Trolls that infect this Forum from time to time in there increasingly desperate bid to rid the world (well actually, just a few bits of Croyden it would seem) - I will answer your question sensibly. Apologies if you are genuine!
Never assume that Tax is logical but I think we can assume that the only way this government is going to tax high polluting cars is to select various emission bands.
That said, most 4x4's are no more polluting than any other vehicle - so choose one that suits your needs and enjoy!
As for a specific 4x4 tax - which is called for by the numpty Anti's - I really do not think that is going to happen with the UK economy now having just one indigenous car manufacturer (albeit now part of Fords PAG, thank goodness) in Land Rover!
And with a Freelander Td4 producing less emissions than popular "urban" cars such as the VW Beetle and BMW Mini - any call for an advertising ban, selective taxation etc would be easily challenged.
Safety is often quoted as a reason not to have a 4x4 by the numpty Anti's - but strangely the LR Defender is apparently the safest car to be in for passengers!
Similarly - if you look at the NCAP website you will see that ALL modern cars are improving their ratings and 4x4's are no different.
The latest Toyota RAV 4 (and excellent 4x4) scores higher than most ordinary cars - in all area - including that of pedestrian safety.
Based on these figures from NCAP - we would be doing the poor "Urban Dweller" a favour if we all went out and bought a RAV 4!