Apologies. Typing gremlin. The date on this original post read 2011. Should read 2002. But in fact the position is more complex.
There are different dates applicable. Diesel vehicles registered before 1st Jan 2006 applies to heavier vans and trucks. Diesel vehicles registered before 1st Jan 2002 applies to lighter vans (there are different dates again depending on whether Euro 3 or Euro 4 currently applies).
Therefore pre-2002 one tonne kerbside/3.5 tonne GVW diesel vans will NOT be compliant come 3rd Jan 2012 and will be subject to a £100 per day charge in the London Low Emissions Zone.
Pre-2006 (1st Jan) heavier vans are also NON-compliant come 3rd Jan 2012 and will be subject to a £200 per day charge in the London Low Emmisions Zone.
Confusing, or what?
Apologies again. Rush to get this out, etc. Should have double checked. But I'm getting conflicting info from everyone, including Transport for London TfL who, it seems, don't agree or understand their own rules.
Check details for yourself. There is a lot of misinformation going around, which is being inadvertently repeated by clumsy posts such as this.
So check the TfL website for the latest and verify the dates. There's bound to be misunderstanding here.
Here are some links. It's a mess of regulations with hidden angles, etc, but you'll get through it with a bit of perseverance.
