The man responsible for admitting students to Cambridge has claimed allowing poorer students with lower grades into the university would be a "cruel experiment" with the potential to "ruin lives."
Outgoing Cambridge admissions office head Dr Geoff Parks said allowing "social engineering" would harm students as they would not not be able to keep up with their peers.
"Our bottom line would be that it actually would be a really, really cruel experiment to take a bunch of students and hypothesise that they have what it takes to thrive at Cambridge and then see them fail because they don't," Parks told the Telegraph.
"We have very high standards within the university and we do fail students in exams."
Parks said Cambridge, which was criticised after it was revealed 42% of its students were educated privately, would not pander to "political imperative."
"None of us in good conscience want to be ruining people's lives on some gut feel or political imperative based around getting votes or pandering to some particular bit of the populace."
Last week the government's new university access chief Les Ebdon said Oxford and Cambridge should broaden their entry standards.
The Office for Fair Access chief told the Guardian: "If the top universities are to retain their positions, they need to access the full range of our society. Otherwise, they are losing a major source of potential."
Universities minister David Willetts has also called for widened access, saying in a speech earlier this year admission chiefs should look at "more than just A-level results, by looking at all the information that indicates the potential of an individual to succeed."