Its good to raise the issue - after all the MOT is undergoing its biggest change for many years on May 20th - bringing us in-line with the EU testing directive. (irrespective of Brexit). There have been some scare stories flying around but i can see nothing in the "new" manual that makes running/using our cars any harder/more expensive or problematic.

A huge change is in the paperwork itself - no longer a simple pass/fail but 4 categories = 1. Dangerous defects 2. serious defects 3. minor defects and 4. advisory items.

A "fail" will be issued for any Dangerous or serious defects but a "pass" can include minor defects. An example of a minor defect is 1 of 2 number-plate lights not working. Confused? I'm assured it will all make perfect sense once its up and running from 20th May.

You are 100% correct about retrospective application of standards - i cannot recall it ever happening. After all it would be very unfair to expect a vehicle to perform better than when it was new. That is why the manual is riddled with date cut off points. Its not possible for instance to fail a 1979 car for a non working offside fog lamp because it wasn't required until some-when in 1980 ( would need to check for actual date!)

There is of course no way your non-cat equipped V8 would pass a 1996 on emissions test ( although it might get close)- hence a 3.5% c.o reading and 1200 HC ppm limit is used.

This used to come up alot with Rover metros and Minis from the transition period - 10 - 15 years ago they were failing the normal cat test often and we had to dip into the emissions standards book to check they needed to - many an L and M reg metro lived to fight another supermarket car-park because of the pre 1st Aug 1995 rule. It still applies today but the metros have gone! Long live the Morgans!

2015 Morgan 4/4 (Wolf fettled) previously 2014 M3W
MINI Cooper S and numerous BMC/BL relics.