"The MOT test in the UK checks emissions" Unfortunately the UK does not have proper emissions checks as part of the MOT. There is a (subjective) visual check

"The MOT test in the UK checks emissions" Unfortunately the UK does not have proper emissions checks as part of the MOT. There is a (subjective) visual check for visible smoke, and a metered exhaust check which again only tests generically for "smoke", ie large particulates. Unfortunately there is no testing of specific pollutants (NOx, PM2.5, PM10, etc) so many vehicles can pass MOT even if they are way outside allowed emissions levels, have had DPF removed, etc.