My sister & Bro-in-Law run a small garage (he ran the paint-shop, but after a heart attack is training an apprentice). My nephew is the qualified, registered, MOT signer. It costs quite a lot and quite some time to qualify. There are 4 other local staff (Calderdale). They have a loyal, local pool of customers who rely on them and their honesty and fairness. (They'll tell someone if a bulb is out and give them a chance to fix it etc..) Many elderly people.
She has told me before now that if the MOT moves to 2 years - they will go out of business. Simple as that. It is the baseline from which they can keep going. So that would mean a lot of taxes gone, a lot of unhappiness and quite a few people out of work.