According to the DVLA its got nowt to do with your pre 2002 engine type but everything to do with the "body type" recorded on your V5C (thats log book to normal peeps). For vehicles after 2002 not contained in the auto exemption list it is up to you to demonstrate that your engine meets the required emmission standards by means of a VOSA test that you will have to arrange and pay for.
If your V5C says "4x4 light utility" in the body type which most Landrovers do because the lazy dealers just use the default when they register them then TFL assume it is a commercial and not exempt - hence the auto checker indicating non-compliance.
TFL dont consider the vehicle make which, if you are lucky, should say "90/110 Land Rover Defender CSW TD...."
This is important because the "Vehicle Make" on your V5C must indicate CSW from first registration in order for the DVLA to change the body type to "station wagon/estate car" which automatically exempts you from the LEZ at the current time as the vehicle is now considered a private car and not a commercial van.
The DVLA told me that, so long as my V5C shows CSW in the "vehicle make" from first registration (which it does) then all I need do is highlight the incorrect "body type" details, fill in section 7 of my V5C with the correct details, sign and date the declaration box, and send it in to the DVLA at Swansea. They say it will be changed and returned within 20 days and TFL will then automatically reference the new details for purposes of LEZ.
I have done this and wait with bated breath the return of my shiny new V5C at which time I'll try the LEZ compliance checker again. If it works I'll be amazed and Red Ken and BoJo can shove their LEZ where the sun dont shine.
If it dont work I'll be on the hunt for some dodgy number plates.
They also told me that they have been flooded with similar enquiries from owners of other makes of 4x4 because the default setting is "light utility" for
all 4x4 vehicles. :doh:
Aren't computers wonderful things?