AN OVERHAUL of the exams system has made it more important for teenagers to think carefully about their A-level choices, top universities have said.

Sixth-formers now have fewer opportunities to try a subject at AS-level before committing to taking the full A-level, meaning their subject picks carry more weight, according to the Russell Group, which represents 24 leading UK institutions including Oxford and Cambridge.

The warning came as the group published its updated Informed Choices guide on the subjects and subject combinations most useful for courses offered by its universities.

"Up to 15 per cent fewer students are taking AS-levels after changes mean they no longer count toward A-level grades," the Russell Group said.

"Students therefore may have less opportunity to try a subject before taking it to A-level and their choices now bear more weight."

Director General Dr Wendy Piatt said: "We are wholeheartedly committed to ensuring our doors are wide open to talented and able students from all backgrounds, but our universities can't offer places to those who do not apply or do not have the right grades in the right subjects.

"Too often, students disadvantage themselves by choosing a combination of subjects at A-level that will not equip them with the appropriate skills and knowledge for their preferred university course.

"Subject choice at GCSE and A-level or equivalent affects everyone's options for degree courses, so we make sure that the most useful and relevant information is available to students everywhere, through Informed Choices."

Under a major shake-up, AS-levels have been separated from A-levels to form a standalone qualification, while new tougher two-year A-level courses with exams at the end are being introduced over a three-year period.