This weekend I got my first Mot done now the car is 3 years old, "f course" nothing was wrong with the car, but the emmisions reading was odd.

It was 0.00, so why the hell am I paying roadtax?

I believe road tax is based on CO2 emissions, whereas for the MoT you will have a smoke test (Looking for soot levels in ppm). As your car will have a DPF to filter out all of the soot then it should read 0.00 (Be worried if it didn't)