The numbers from these backgrounds are likely to rise after the introduction of tuition fees of up to £9000 south of the Border, according to Professor David Raffe of Edinburgh University.
The professor in Sociology of Education spoke out as Scottish universities recorded an increase in the number of fee-paying students from England, Wales and Northern Ireland.
Figures from Ucas, the body that administers higher education admissions, show the sector has seen a 9% hike in students from the rest of the UK (rUK), with 4700 already having secured a place.
However, while universities from elsewhere in the UK are compelled to invest in bursaries and scholarships as part of the introduction of fees, Scottish universities are not.
Universities Scotland, which represents principals, has argued that institutions offer the most competitive support package in the UK, worth some £3 million in rUK bursaries and scholarships.
However, student body NUS Scotland and the UCU lecturers' union have both called for statutory measures to ensure bursary levels are maintained.
Mr Raffe said: "In the past, students from the rest of the UK studying in Scotland ... have been disproportionately well-qualified and middle class, often from independent school backgrounds.
"It would be unhealthy if, after the introduction of higher fees, national differences between students correlated even more strongly with differences in social and educational backgrounds.
"We need Scottish universities to consider what can be done to widen access not only to those students who live in Scotland, but also to those coming to study here from other parts of the UK."
Alastair Sim, director of Universities Scotland, which represents university principals, said institutions wanted to attract the brightest and the best students from the UK "whatever their social background"
He said: "We are confident that Scotland's universities have put in place a highly competitive package of means-tested bursaries and other financial support to ensure that cost is not a barrier to potential applicants from England, Wales or Northern Ireland."
However, Gordon Maloney, president of student body NUS Scotland, said the organisation was opposed to charging students.
He added: "Students coming to Scotland from the rest of the UK are at the whims of their university as to how much, or little, financial support they receive."
Dave Anderson, president of UCU Scotland, which represents academics, said lecturers were opposed to "profiteering" by institutions. He said: "Scottish universities are making millions by charging other UK students and bursaries for the less well-off are not regulated."
Fees were introduced by Scots universities for rUK students in 2012/13 as a result of policy changes in Westminster.
Since then, universities have been actively marketing themselves south of the Border.
Meanwhile, Scottish universities have been set challenging targets to widen access to students from poorer backgrounds under a Scottish Government policy.