Highly selective universities will have to fight over an ever-smaller number of students because of the dwindling university-age population and the rise of vocational qualifications, the chief executive of Ucas has warned.

Mary Curnock Cook argued that in 2020, there would be about 130,000 fewer 18-year-olds than in 2009 in the education “pipeline”, a big reduction in the number of potential students.

Assuming that 40 per cent go on to university, in 2020 each university will have about 200 fewer students than it has now, she said. “These are very, very big numbers in university admissions.”

Government reforms that allow the unrestricted recruitment of students who achieve grades ABB at A level will leave highly selective universities particularly vulnerable, she told delegates at the Council for Advancement and Support of Education Europe conference in Manchester on 28 August.

The ABB policy means that such institutions had to attract a sustainable number of high-grade students every year, rather than being allocated a certain number of places to fill, Ms Curnock Cook explained.

Although the proportion of 19-year-olds holding A levels had remained flat over the past decade, the proportion doing vocational qualifications, chiefly BTECs, had increased fivefold, she said.

In addition, with proposed reforms to A levels expected to make the qualification harder, “fewer people [will] do them”, she said.

“The selective universities that are competing at that top end in this high-grade policy are actually – still slightly unbeknown to them – competing for a small proportion…of a smaller population,” she said. As a result, there will be “increased competition for a smaller number of high-grade students”.

Universities with lower entrance tariffs were increasingly recruiting applicants with vocational qualifications, but the selective institutions were “tied in” to high-grade A levels.

“This is not a nice place to be, I would suggest, for selective institutions,” she said.

Ms Curnock Cook has already warned that a decline in top grades at A level could cause serious problems for institutions relying on ABB students to fill their courses.

The decline in grades awarded this year “could leave 30 or so higher education institutions with at least 100 fewer ABB+ recruits than expected”, she wrote in Times Higher Education last week.

Figures from Ucas last month show that 2013-14 undergraduate recruitment has recovered to 2011‑12 levels after a dip following the introduction of higher tuition fees in 2012‑13. But Ms Curnock Cook had a “word of warning” for universities cheered by the better figures.

“This year you’ve managed to get more [students] in at 18,” she said, but added that “you might pay for it” in 2014-15 because there would therefore be fewer 19-year-olds to recruit in that cycle.

Ms Curnock Cook also remarked that the clearing process was no longer used to recruit “the dregs” any more, and speculated that it could even remove the need for an admissions system based on students’ actual, rather than predicted, grades.

“Every year I get asked: isn’t it now time to go for a post-qualifications applications [system]? My answer is that we already have PQA: it’s called clearing,” she said.

david.matthews@tsleducation.com