Unless I have misunderstood the proposals, this looks like nothing more than making it illegal to delete the emissions control functionality that a car was fitted with when new. As such, all it does is to close a loophole.
Have I misread it?
Pretty much! Although it's not just deliberately manipulating emissions:
"
We have chosen not to distinguish between excess emissions caused by poor maintenance of a vehicle and those caused by modifications made to vehicles."
My reading is that the MOT standards haven't been updated since Euro 4. Cars built to Euro 5 and 6 standards aren't tested to those standards. The proposal is to change the MOT system to use the standard in force when the vehicle was built, rather than the current method of periodically updating the law to cross-reference the Euro standards:
"
This means that the following will be prohibited:
using a vehicle on the road which has been maintained or modified in a way that means it no longer meets the emissions standards that it was approved to"
In other words, closing the current loophole and making sure it doesn't reappear at the next Euro standard update.