The original NPPL Medical Declaration system did at least require the pilot to visit an AME to countersign the certificate. There were 2 grades, one which permitted flight with passengers and one which did not.
Sorry Beagle but you are incorrect. The NPPL declaration was signed by your GP, who arguably had full access to your medical history. If you wanted to carry passengers you had to meet the standards for DVLA Group 2 (HGV/Bus/Taxi driver)