A paper by Chris Havergal in Times Higher Education. Some quotes:
The first-ever release of Ucas data at institutional level shows that the University of Cambridge admitted only 65 18-year-olds from the UK’s most disadvantaged neighbourhoods in 2015, while it gave places to 1,260 learners from the most advantaged backgrounds. Taken as a proportion of the total size of these groups, this meant that the most privileged students were 16 times more likely to win a place.
The overall ratio for the Russell Group of highly selective institutions was 7.7, but this remained significantly higher than the UK-wide average of 2.45. At providers with the lowest entry standards, the most privileged students were only 12 per cent more likely to get in.