[highwaylights]

There’s plenty of blame to go around, diesel filters aren’t checked for at MOT and (as an example) it’s quite easy to buy a passing result as the garages responsible for servicing your car are the same one carrying out the test (and offer guaranteed pass packages so they would also bear the cost of putting anything right that failed - so they’re strongly incentivised to ignore problems).

That all said, testing wasn’t mandatory for most of Covid and emissions aren’t really tested properly even though they were supposed to be years ago (emissions tests won’t detect removed particulate filters if you don’t accelerate during the test, so the garage that just took a bribe to remove your filter can choose not to do that and wave you on through).