This excellent article describes in detail a new three-tiered rating system of teaching quality at universities introduced by the U.K. government, as well as a thoughtful discussion. As I have a son and daughter-in-law teaching in a U.K. university and grandchildren either as students or potential students, I have more than an academic interest in this topic.
How are the rankings done?

Under the government’s Teaching Excellence Framework (TEF), universities in England and Wales will get one of three ‘awards’: gold, silver and bronze (apparently there are no other categories, such as tin, brass, iron or dross for those whose teaching really sucks). A total of 295 institutions opted to participate in the ratings.