According to The Economist (August 10, 2017), Royal Holloway ranks second amongst UK Mathematics departments for value added, by which they mean the difference between estimates of expected earnings and the actual average salary of their graduates.

The statistical model that estimates how much graduates from each university can expect to earn is based on how selective a university is, what subjects its students study, the share of students from lower-income areas, how many students enter after age 20, what share of students attended private schools and where the university is located. 

The full article is available here.