Ok, some may know about this, others propably haven't a clue.
As per Next Feb 2008, there is going to be a Low Emission Zone inside the M25. The website here
To summerise effects Lorries and will affect Vans that basically pollute the environment with their DIESEL emissions, Petrol is not effected. Check your vehicle and area on the site.
This is not a cheap option by the way, £200 fees for Lorries and £100 for vans.
THIS DOESN'T AFFECT CARS!!!
Not a pimp or advert but more a useful bit of information for those people that visit the Big City in their polluting motors.