Only 42 per cent of grades predicted by teachers in 2010 were correct when the final results were published, according to a Department for Business, Innovation and Skills research paper published on 5 November.

That compares with a 48 per cent accuracy rate reported in a study released last month, which tracked the results of students taking the OCR exam board¡¯s A levels in summer 2012.

The BIS study, titled Investigating the accuracy of predicted A level grades as part of the 2010 UCAS admission process, is likely to re-ignite questions over the fairness of the UK¡¯s university applications process, where offers are often based on predicted grades.

Plans for post-qualification applications (PQA) were ditched by Ucas in March 2012 after they received a hostile reception from universities.

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It may also raise questions about plans to downgrade AS levels to optional exams from 2015 because many admissions tutors claim they are a more reliable guide to achievement than predicted grades made by teachers.

The report reviews about 177,000 predicted A-level grades in the 2010 admissions cycle ¨C about a third of A-levels taken by those applying to higher education.

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It found teachers were more likely to over-predict student grades, with 48 per cent of predicted grades ending up higher than the achieved result.

Only 11 per cent of predicted grades were under-predicted, with students exceeding teacher expectations.

That trend was particularly stark when it came to the new A* grade, which was introduced in 2010 and is used by some highly-selective universities, including Oxbridge.

About half of those predicted an A* only achieved an A, while 12 per cent predicted an A received the higher grade, the report says.

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The introduction of the A* also worsened the accuracy of teachers¡¯ predicted grades compared with previous years because an A was once the most easy grade to predict correctly.

Accuracy rates for predicting an A fell from 64 per cent in 2009 to 43 per cent in 2010, the report says. For all grades in 2009, the accuracy rate was 52 per cent, which fell to 42 per cent in 2010.

jack.grove@tsleducation.com