[mnw21cam]

I don't think "enormous costs" is a strong argument here. The annual MOT is usually under £50, and that includes a fairly comprehensive roadworthiness check and emissions check. A stronger argument would be that a car owner could change some settings on their car specially to pass the emissions check, and then set them back to dirty afterwards each year.

[Arainach]

An MOT is a cost to every driver every year - significant in money and in time - plus the cost of running the infrastructure to provide the testing. All so that a few people can tune engines? No thanks.

[mnw21cam]

It's not just so that a few people can tune engines. The majority of the MOT is the roadworthiness check.