A York University analysis found that first-year physics undergraduates now start university with significantly poorer maths skills than their counterparts 10 or even 20 years ago.
Students in 1979 scored around 75 per cent in the university's own maths test taken by all new physics students - compared to just over 50 per cent in 1999.
The scores stayed roughly constant until 1990, then began to fall rapidly.
A study by Coventry University also found A-level maths suffered "grade dilution" of a grade every two years in the 1990s.
Advanced General National Vocational Qualification students have much poorer maths skills than A-level students, it found.
Students who failed A-level maths did significantly better in Coventry University's own maths tests than those who had passed Engineering Advanced GNVQ.
Boh universities set their own maths tests for first-year undergraduates. The results are used to find students' weaknesses so lecturers can help them catch up.
Dr Duncan Lawson, director of Coventry University's BP mathematics centre, said: "This has serious implications for many engineering courses. The latest advice from the Engineering Council specifically identifies Advanced GNVQ as an acceptable alternative to A-level as an entry qualification for accredited degree courses. However, the mathematical experience of Advanced GNVQ students is vastly different to A-level."
The studies are part of a new report blaming changes in GCSE and A-level syllabuses and fewer A-level or further maths students for the decline in the skills of students accepted for degree courses.
The report says more universities should follow Coventry and York's lead and set diagnostic maths tests new undergraduates.
Measuring the Mathematics Problem: www.engc.org.ukgateway3