I doubt very much whether the MOT test is to blame for the
failures,although I do believe that there ought to be another way to check Diesel emissions.
VOSA had to change the test as originally you were suppossed to hold the engine at maximum revs for something like 10 seconds.This had to be changed as engines were exploding left,right and centre!!
When we do the test(maximum revs up to 6 times in a row)
the engine is at normal running temperature(usually 60 degrees C
temperature) so as to limit the potential for problems.We also have to ask the customer questions regarding when the car has been serviced last and whether the cambelt has been replaced at the correct intervals.
In my opinion you should drive a diesel hard periodically to clear the system out which will allow it to run more efficiently and result in your car going through the emissions test easier.
I have tested 1000's of cars and never had any problems with turbos or intercoolers etc.The problems that Renault have are specific to them,and it has to be a design fault in their system somewhere.It would be nice if they'd just admit as much,but I doubt very much they ever will.......