Predicted grades should not be used by universities to make offers to students, a union has said.
The UK is "out of step" with the rest of the world on university admissions, according to the University and College Union (UCU) which is calling for an overhaul of the system.
Currently, institutions use a potential student's predicted grades, typically for A-levels, when deciding whether or not to offer them a place on a degree course.
The place is then confirmed on A-level results day, once a student has their final results.
But the UCU argued that the UK is the only nation which uses predicted grades, noting that research has previously shown that as few as one in six A-level grade predictions are correct, and suggesting that the system encourages the use of unconditional offers, whereby students are awarded places regardless of their grades.
Research commissioned by the union, published today, examines university admissions in 29 countries, plus England, Wales and Northern Ireland.
It concludes: "No country in the study, with the exception of England, Wales and Northern Ireland, has a system of pre-qualification admission where the offer of a place in higher education is based on the results the student are predicted to achieve.
"England, Wales and Northern Ireland are real outliers in terms of their reliance on predicted grades to determine how prospective students are offered higher education places in comparison to the diverse range of countries featured in this study."
The findings come just weeks before students learn whether they have scored the A-level results required for their university places.
UCU general secretary Sally Hunt said: "We are alone in the world in using a system where students are offered university places based on highly inaccurate predicted grades."
She added: "Unconditional offers have made a mockery of exams and led to inflated grade predictions, while putting students under enormous pressure to make a snap decision about their future.
"The simplest and fairest way to deal with these problems is for us to adopt a system of post-qualification admissions, where offers are based on actual achievement rather than estimated potential, as the rest of the world does.
"It's time for the Government to give the system the urgent overhaul it needs."
Malcolm Trobe, deputy general secretary of the Association of School and College Leaders (ASCL), said: "ASCL echoes the concerns in this report about the use of predicted grades to award university places and calls on the Government to review the system urgently. Out of date and no longer fit for purpose, it is a historical quirk which is not mirrored in other countries and creates unnecessary problems."