Pete
That link is for a story in May 2004. So any news from it will have moved on in both directions now.
The problem with higher tax for 4x4 is that it will make the problem worse in towns not better. We live in a materialistic world and as such many see the fact that what they drive as a "what I am worth" statement. If tax is higher for a certain kind of vehicle then these people will buy more of them to make a statement.
This is an honest answer - To me, it will not matter as I need the car and the money is not a big issue. However, for a lot of people who need to drive 4x4's for business, Towing or for access to the countryside, they will be hit hard. The Chelsea tractor set will just see it as a hike in the "status" of their car.
Some people have suggested that a "need" based tax be put into place, again this would be no use in controlling the real issue as the people who use them for the 100m school run will just buy a caravan and have it stored. (or use another one of the many loop holes that will become apparent)
What is really needed is a good set of realistic laws and benefits.
Suggestions would be -
you must fit mirrors to make all sides of the vehicle visible while reversing as they do in hong kong
Massive tax cuts on greener fuels (this helps people who need it and sends a message of "I cannot afford the fuel" to the snobs friends thus reducing there perceived value
Councils and landowners made to maintain their rights of way at an agreed level. This will reduce damage in the countryside and give real guidelines on the use of vehicles off road.