Sorry, but that is bollocks. If a vehicle is not compliant with all ECE regulations, then it is breaking the law. Also this document from the DfT
595099 EYE BOLT | shop | www.lrseries.com | L. R. Series is dated from 2010 so it was illegal in 2010 to have HID lights fitted without washer and self levellers. so this legislation pre dates the 2012 rules you keep spouting. The MOT test is a basic test of roadworthyness at the time of the test and does not cover all ECE regulations, nor does it test whether or not a vehicle is fully type approved. The simple fact is that if a vehicle that does not comply is stopped and inspected, then the driver may find themselves liable to prosecution. the fact that the law is not always enforced does not mean the the law does not apply.