I asked my local dealer to give me a reading of my car's actual emissions (it's 2 years old) and to compare it with what the manufacturer says it should be and what the MOT test requires for a pass.
Firstly, they admitted that their testing machine is not really up to the job. (This is a Volvo main dealer......)
Second, they took the car to an MOT testing station and got the printout, which was a PASS as expected.
Thirdly, no-one understands the details printed on it, so I still don't have my question answered!
So, the conclusion is that whilst I would like to know how good or bad the emissions of my car actually are compared to the statistics for it and the law, no-one knows how to work it out anyway. Therefore, emissions testing is clearly too complex and that what the manufacturers quote for new cars has nothing to do with what your car actually produces. AND they base your tax on these figures!!