Only 21 per cent of English 18-year-olds who were expected to get grades ABB matched or bettered that prediction in 2014, compared with 32.2 per cent four years previously, according to the latest End of Cycle report from Ucas.
This meant they were 34.7 per cent less likely to achieve their predicted grades.
For those predicted AAB, the proportion attaining ABB or better fell from 58.4 per cent in 2010 to 46 per cent in 2014, a 21.2 per cent drop proportionally.
Students predicted to get AAA were 12.7 per cent less likely to achieve ABB or better, with the proportion of 18-year-olds in this group meeting this mark reducing from 85.5 per cent in 2010 to 74.6 per cent in 2014.
The figures may partly explain the continuing fall in the proportion of university applicants entering the most selective institutions with the highest grades.
The proportion of English 18-year-old students entering “higher tariff” universities having achieved the equivalent of ABB or better at A level fell to 82 per cent in 2014, after a high point of 89 per cent in 2011.
Among students who got BBB, 35 per cent entered a higher tariff university in 2014, compared with 17 per cent in 2011.
However, there is some evidence that universities are becoming more discerning about who to admit when applicants do not do as well as expected. The number of students accepting a place at their insurance choice institution in 2014 increased by nearly 12 per cent year-on-year.
The Ucas report adds that attainment of higher than predicted grades is “relatively rare”.
In 2014, only 6.9 per cent of students predicted BBB went on to achieve ABB or better. This compares with 12.3 per cent in 2010.