Leading universities such as Edinburgh, Birmingham, Sheffield and University College London said students were often banned from retaking an entire A-level to get on to some of the most sought after degrees such as law and medicine, writes Graeme Paton at the Telegraph.
With competition for higher education places at a record high, it is believed that as many as a third of the 707,000 university applicants this year will fail to secure a degree course.
It is believed that many will reapply next year, even though annual tuition fees will soar as high as £9,000 for students starting courses in 2012.
The Council for Independent Education, which represents colleges specializing in A-level resit courses, said the number of enquiries to its members had doubled in July compared with the same period in 2010.
At present, students can resit individual A-level modules or retake an entire year. It is believed that between 30 and 50 per cent of pupils retake some papers.
But head-teachers warned that the sheer complexity of universities' rules on resits risked damaging the career prospects of thousands of students.
Tim Hands, master of Magdalen College School, Oxford, said:
"The more complex it is to get into university, the more it is going to deter people from going at all, particularly if they have not got access to the kind of advice they need to negotiate the applications process."
Neil Roskilly, from the Independent Schools Association, added:
"There are often valid personal reasons why a student has taken resits and there are not always opportunities to make that known."
But Steve Boyes, chairman of the Council for Independent Education and principal of Mander Portman Woodward College in west London, said: "Once again demand for retaking will be very high.
"This may seem surprising with some vice-chancellors preparing for a collapse in the number of applications next year, due to the higher university fees payable in 2012. On the other hand, just like last August, there are going to be more than 200,000 disappointed applicants this year, and a good proportion of these will want to re-apply with better grades."
The Daily Telegraph gained data from almost 70 universities across Britain on their applications policies. The majority said resits were judged in the same way as first-time exams. Others said they devolved decisions in the issue to individual subjects departments.
But the most selective universities often exercised more control. UCL said a "limited number" of courses – notably medicine and law – expected A-levels to be sat in a standard two-year cycle.