Students at Oxford and Cambridge have been accused of elitism for not taking part in a national student survey.
The government-backed survey measures student satisfaction
Vice-chancellor of Leeds University Michael Arthur said Oxbridge students should show a commitment to the survey which measures student satisfaction.
The National Union of Students said the approach reinforced the image of Oxbridge as a "bastion of exclusivity".
The student unions at Cambridge and Oxford are boycotting the survey, saying it is "over-simplistic".
The student unions believe the questions in the survey are not ideally suited to cover the complexities of a collegiate system.
The criticism of students at the universities was made to the cross-party Commons Education Select Committee on Monday.
Oxford, Cambridge and Warwick
For the past two years, both Oxford and Cambridge have not been included in the government-backed national survey of student satisfaction levels.
The universities did not get the required minimum of 50% of final year undergraduates to complete the survey forms.
Professor Arthur told MPs: "Inevitably a few institutions drop down below that (50%) threshold.
"There are three institutions where students' unions have actively boycotted the National Student Survey, those are the universities of Oxford, Cambridge and Warwick.
"We have been working hard on trying to persuade them to participate. I think we have had some success with the University of Warwick.
"I think I would describe the University of Oxford now as being at least neutral and the University of Cambridge is actively boycotting the survey this year.
"I personally think it's a great shame that they have done that because this is an opportunity for their students to say what they want to say about the institutions."
He went on: "I am a little bit concerned about widening participation issues at those universities.
"If they have got students who are coming from low income families who go on to the website and can't get information, I can imagine that that would put them off."
The National Union of Students vice president Wes Streeting told the select committee: "In the case of Oxbridge in particular, I think they have issues to deal with in terms of the ongoing myths that exist around the admissions system - the notion of the old school tie and secret handshake.
"They will do themselves no favours when applicants click onto the Ucas website in the future and find that they can find student satisfaction data for every higher education institution in the country except Oxford and Cambridge.
"I think that sends a very worrying signal."
Low response rate
A spokesperson for the University of Oxford said the university had not refused to participate in the national student survey - rather its results were not published.
"A low student response rate to the questionnaires meant that NSS did not want to publish results from Oxford, although the university would not have objected the publication," she said.
"Concerns have been raised in the past within the university and the Student Union about the ability of a generic survey to provide sufficiently precise information about the individual courses at Oxford or to reflect accurately the particular student experience at Oxford."
The University had its own questionnaire designed to monitor undergraduate students' learning experience of their whole course, she added.
A spokesman for Cambridge University said all final year students were asked to complete the survey.
"Pro-vice chancellor for education Professor Melveena McKendrick wrote to all final year undergraduates on Friday 26 January 2007 advising them that, while the National Student Survey is not ideally designed for the complexities of a collegiate university, it is here to stay.
"'It would be a glaring omission', she wrote, 'for Cambridge to be the only university not to have its results posted along with those of other institutions when prospective applicants are making comparisons', and she encouraged students to participate."
But Cambridge University Students' Union is urging its members to boycott the survey because its questions are "over-simplistic to the point of meaninglessness".
"Despite the good intentions of the survey, its implementation has been a disaster," the union said.
"It produces meaningless data which is gathered in an intrusive way."