The University of Cambridge is Britain's most unequal university, according to a new education briefing.
It is followed by St Andrews, Bristol, Oxford, Aberdeen and Edinburgh, the Higher Education Policy Institute (HEPI) policy note found.
Of the top 10 most unequal institutions to study at, Russell Group universities accounted for seven places.
At the other end of the scale, the University of Hull was found to be the most equal.
The new briefing, Benchmarking widening participation: how should we measure and report progress?, looks at each university's success in widening participation and ensuring access to people from all backgrounds.
It calculated the ratings based on universities' share of students coming from different POLAR quintiles, which are used to measure how advantaged an area is.
Director of HEPI Nick Hillman said: "Tackling the challenge is fraught with problems.
"The biggest obstacle is probably a fear among parts of society that have historically dominated our most selective universities that they could be squeezed out."