категория диплома\ итоговая оценка (итоговый балл)

https://www.multitran.com/m.exe?a=3&sc=323&s=degree class&l1...
first-class honours degree - диплом первой степени (Система оценок в Англии. Итоговая оценка 70% и более Johnny Bravo)

почитайте о системе ВО в UK
http://dereksiz.org/uchebno-metodicheskoe-posobie-dlya-aspir...
University and Higher Degrees in Great Britain
In England, Wales and Northern Ireland the most usual titles for a first degree are Bachelor of Arts (BA) or Bachelor of Science (BSc). A first degree is usually awarded at the end of a three-year course, which most people start at the age of 18/19, after leaving school, a second degree is Master of Arts (MA) or Master of Science (MSc) and a higher degree is Doctor of Philosophy (PhD or DPhil).
A higher degree is one which is awarded after further study, usually, although not always, involving research.

After a course of studies lasting from three to four years an undergraduate student sits for a final examination which, if he passes it, entitles him to a first degree. The final exam is the principal criterion for establishing the class of degree.

Until recently, postgraduate Master’s degrees were awarded without grade or class. Nowadays, however, Master’s degrees are classified into categories of Pass, Merit and Distinction – commonly 50+, 60+, and 70+ percent marks, respectively.

https://megaobuchalka.ru/5/29671.html
The first stage lasts for three or four years and leads to the award of a Bachelor's Degree in Arts, Science or other fields (Technology, Law, Engineering, etc.). It is now rare for the class of degree to depend entirely on student performance in final examinations. Most institutions base a component of the degree class on examinaions taken during the period of study, especially those taken at the end of the second year, and many also use some form of continuous assessment.

https://en.wikipedia.org/wiki/British_undergraduate_degree_c...


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Note added at 17 hrs (2020-02-19 13:15:20 GMT)
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Да, похоже, что "степень отличия диплома" - это один из вариантов перевода термина Class of degtree. Насколько он удачен, сказать сложно, поскольку в нашей системе высшего образования такой градации нет (если не считать "диплом с отличием"). Перевод лучше выбрать тот, который не потребует каких-то дополнительных разъяснений.

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Note added at 19 hrs (2020-02-19 15:05:50 GMT)
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Пожалуйста! Форум для этого и предназначен.