Teenagers who take vocational A-levels only do fractionally less well at university than those who take the traditional version of the exam - provided their previous academic results are comparable.

The finding, from a report to be published next week by the Higher Education Policy Institute, is likely to be seized on by both critics and defenders of vocational courses, and will raise questions about how well the new 14-19 diplomas can prepare pupils for university.

The institute examined the progress of students who took vocational A- levels and found that they were significantly less likely to get a high degree classification than those who sat the traditional exams. They were also as much as 50 times less likely to attend one of the prestigious Russell group universities.

When the academic A-level group was weighted to match those who took the vocational exams, by matching their results and choice of subjects, the gaps narrowed. Only a one percentage point difference existed in their likelihood of getting a first-class degree, and both groups saw the same proportions get thirds or unclassified results.

However, those who took vocational A-levels were five percentage points less likely to get a 2:2 classification and were three percentage points more likely to drop out.

They were also five times less likely to attend a Russell group university and three times less likely to attend one established before 1992.

The report suggests that there are many reasons why these students attended different universities. Among the explanations were that admissions tutors did not regard the Ucas scores for vocational and academic A-levels as equivalent, suggesting they needed to be recalibrated. Or that the universities recognised that some of their degree programmes might not be suitable for students who “do not have the academic grounding that academic A-levels provide”.

“It suggests that good careers and academic advice is essential for students post-GCSE as they are deciding what to do at level 3,” the report states. “Wrong choices at this stage may rule out certain options later.”

The report is to be published at an institute conference in London on Tuesday, sponsored by The TES, which will examine developments in higher education applications and their implications for schools.

Bahram Bekhradnia, director of the institute and co-author of the report, said the difference in degree results was significant. “With samples of this size you would expect no difference at all when allowance is made for the differences in tariff score and subject of study,” he said.

“My guess is that the Ucas tariff is miscalibrated and, for example, someone with a B in VCE (vocational certificate of education) is not as able as someone with a GCE (general certificate of education) B, but they get the same number of tariff points.”

Details of the conference on `Developments in Higher Education Applications and Admissions: Implications for Universities, Schools and Colleges’ at www.hepi.ac.uk.