This could be the end

[C.A.R.]

Parts as you say are already made to a certain 'standard' but bespoke modifications whether carried out by a garage or budding ameteur mechanic are not really 'approved' of, but no legislation currently makes them illegal.

The government will be happier when everyone is driving around in a white, silver or grey car with <99g/km emissions. This way emissions are effectively controlled by the government, by making 'dirty cars' illegal or passing legislation which makes them apparently unsuitable for the roads will eventually filter people like us out, we will be driven into owning these 'appliance cars' forever more, because cars and driving aren't things we should be enthusiastic about, they are merely a means of getting from A to B.