All the UK university ranking systems use basically the same data — the National Student Survey (NSS) which measures students' impression of teaching quality, the Graduate Outcomes Survey (GOS) which measures employment 15 months after graduation, and a bunch of standard data collected by HESA — entry standards, whether students complete their degrees, average degree classifications, etc.

Much of this data is extremely 'gameable', and a lot of the 'alpha' between successful and less successful institutions is being 'good at surveys.' e.g. for NSS, between comparable institutions it's really a question of how good they are at getting students to complete the survey (students mostly ignore it, and you lose marks for poor completion rates).

Of course — it should also go without saying that there is no 'correct' weighting for any of this data, and depending on how you weight the different indicators, the rankings change.