As others have said...he should stick to...well, not sure really.

If he thinks there is a problem with a car that is running perfectly fine, then maybe he shouldnt be MOT'ing cars !

And what a load of nonsense that older pre-cat cars should be 3% CO. 1983+ they must be below 3.5% CO and 1200ppm HCC to pass the MOT test, but that certainly doesnt mean they should run at 3%