Parity of esteem between vocational and academic qualifications remains a myth, according to new research.
Students with purely vocational qualifications have a much higher risk of not obtaining a place in higher education and of dropping out after their first year, academics at the University of Oxford have found.
Such students are also heavily underrepresented in higher-status universities.
However, students who combine academic and vocational qualifications are nearly as successful at entering and completing higher education as those with academic qualifications only.
The proportion of students entering higher education with purely vocational qualifications decreased from 14 per cent to 10 per cent between 1995 and 2004, while the proportion with a mixture of vocational and academic qualifications rose from 4 per cent to 14 per cent.
Geoff Hayward, lecturer in education at Oxford, who is co-director of the Economic and Social Research Council project, funded by the Higher Education Funding Council for England, said: "The implications of this for (the Government's new 14-19) diplomas are really quite profound. It would suggest to me that young people need to think very carefully about what they do in addition to the main learning of the diploma, in the 'additional specialist learning' slot.
"This evidence suggests that they really do need to put an academic qualification in there if they are going to maximise their chances of progressing into higher education.
"Good information and guidance is going to be absolutely crucial - messages from institutions on entry requirements need to be made very soon."
The researchers also found that while lecturers were very interested in vocational qualifications, their knowledge was often limited.
"We still have a qualifications jungle in this country, and to expect lecturers to become familiar with the full range of vocational qualifications in existence, given the many demands on their time, is just not realistic," Dr Hayward said.
He added that if the new diplomas proved effective they could help simplify the system.