British undergraduate degree classification
In the United Kingdom, medicine is usually taught as an undergraduate course, with graduates being awarded a master's level qualification: normally the conjoined degrees of Bachelor of Medicine, Bachelor of Surgery (MBBS, BM BCh, MB ChB, etc.) although at Queen's University Belfast (and universities in Ireland) Bachelor in the Art of Obstetrics (BAO) is added, and at some universities only the Bachelor of Medicine is awarded - all of these have equal standing. Unlike most undergraduate degrees, the MBBS is not normally considered an honours degree, and thus is not classified into first class honours, etc. Students may be awarded "Merits" and "Distinctions" for parts of the course or the whole course (depending on the institution) and "Honours" may be awarded at some institutions for exceptional performance throughout the course (as a grade above Distinction).
Diploma of Higher Education
The Diploma certifies that a student has achieved a minimum standard for 2nd Year courses in science and liberal arts. If a student is undertaking a full Bachelor of Arts, a Diploma of Higher Education marks two-thirds of their undergraduate degree. Thus allowing the British Diploma to rank ahead of the American Associate of Arts (which in American parlance is a two-year undergraduate, or half of a BA/BS). That being said, American universities generally consider UK Diplomas equivalent to a college level Associate of Arts even though a British student typically holds more credit hours (and therefore more study time) in the arts, humanities and/or sciences.