And engine swaps. Remember that guy who put a Cosworth YB in his Zetec? To be fair, that car had... problems, but it sounds like even a successful transplant would be an issue if the Gov maintains a model database and measures your motor against the manufacturer's figures for your car's factory spec.
Presumably most C1 Cougars won't fall foul of this (with a pre-2001 build date) but I wonder if - as Tony suggests - the maximum allowable cost of an MOT (currently £54.85, apparently) will go up for all of us, to pay for the added kit that MOT stations will need.
Lastly, this is only a "Consultation" and no law has yet been proposed. And even once it is, public-facing Gov IT projects over-run constantly and catastrophically. I'll probably be dead before they bring this in.