when roadside emmissions were mentioned in this thread, I did a bit of searching on the net.
if you go
here and scroll down and download the "
Roadside Emissions Testing - summary of findings" which is the results from 2002 to 2004 testing, it states the following:-
"During the period 2002 to 2004, approximately 25,196 roadside emission tests were undertaken through local authority activities"
"The lowest failure rates were associated with petrol catalyst equipped vehicles (3%), while the highest overall failure rates were associated with the non-catalyst equipped petrol cars (8%). Failure rates amongst diesel vehicles were also high at between 6% and 7%. For those manufacturers with sufficient sample sizes, the highest failure rates were associated with Rover and Lada. However, these samples were dominated by relatively old vehicles and models. LTI and Metrocab, both major suppliers of UK taxis, show average failure rates of 24%. Failure rates for taxis overall were a major concern, given their high mileage and urban concentration."