The rising numbers of first-class degrees awarded by universities make them look like they are "dumbing down", a leading Liberal Democrat says.
The number of firsts awarded by most leading universities was up
The Russell Group - composed of 19 leading universities - gave firsts to 15.5% of students last year, compared with 11.8% in 1998.
Lord Oakeshott, a Lib Dem peer, said these could become "devalued currency".
He has written to the Education Secretary, Charles Clarke, asking him to explain this "drastic rise".
From 1998 to 2003, the proportion of first and upper-second-class degrees awarded by Russell Group universities rose from 61.1% to 66.6%, according to the Higher Education Statistics Agency.
Lord Oakeshott said: "Students and prospective employers need assurance that degree standards are reliable and stable, not devalued currency.
"It is difficult to believe that there has really been such great leap
forward in academic achievement. There must be something causing the
universities to ease off the students.
"Is the government aware of these figures and, if so, is it doing
anything about it?"
The figures show Cambridge University awarded the highest proportion of first-class degrees last year - 32.9%, up from 28.2% in 1998. Oxford was next with 23.4%, from 17.2%.
Glasgow had the lowest rate at 9% - down from 10.6%.
Warwick, however, saw the proportion of students gaining first-class degrees almost double from 10.6% to 20.3% during the five years.
A spokesman for the university said: "It is no surprise that our results are getting better.
"Forty years ago the university site was farmland. We have risen rapidly from being somewhere that sheep grazed to become one of the top five universities in the UK.
"We are becoming more and more popular and we are attracting better candidates. Lord Oakeshott should come and see what we have achieved."
A Department for Education and Skills spokesman added: "It is a matter for universities to develop the qualifications outcomes of their students.
"The overall standards of higher education qualifications are safeguarded by a sector-wide quality-assurance system which is second to none."
A spokesman for the Quality Assurance Agency, which looks after standards in higher education, said: "Universities are responsible for their own academic standards, which they establish in the light of comparisons with other institutions and national guidelines.
"Exam results are criterion-referenced rather than norm-referenced, so it is entirely possible that the number of first-class honours degrees can increase without a reduction in standards."
The members of the Russell Group of research-led institutions are: Birmingham, Bristol, Cambridge, Leeds, Liverpool, King's College London, London School of Economics, Newcastle, Nottingham, Oxford, Sheffield, Southampton, Edinburgh, Glasgow, Cardiff, Warwick, Imperial College, University College London and Manchester.