A GCSE student saw their result in one subject jump six grades after it was reviewed following last summer’s results day.

A newly published report by exam regulator Ofqual blamed a marking error on one unit for the mistake, while an “administrative error” resulted in another student’s AS level result going up by five grades.

They were among a total of 401 GCSE, AS and A levels awarded last summer which were changed by two grades or more after results day.

These included 18 awards that rose by three grades, and three by four grades.

The figure of 401 represents less than 0.01 per cent of all 6,687,000 qualifications given last year, and is a fall from the 639 results that changed by two grades or more the year before.

However, today’s report says that despite the low numbers they “represent unacceptable error in the system”.

Marking errors were blamed for 51 per cent of the changes in marks, with issues with the original moderation cited in another 39 per cent of cases.

The research says that changes of two grades or more are most common in English (115), art and design (100), religious studies (41), geography (24), and history (17), and adds: “This is likely to reflect the structure and nature of these assessments, since some assessments are inherently more subjective than others.”

Changes of two grades or more were most common in GCSE full courses, where there were 165 cases, and AS levels, with 156, although the report says this can probably be partly explained by greater number of entries for these qualifications.

At A levels and GCSEs, most changes saw a student who originally received a B move up to an A*, while at AS level, most involved a student going up from a C to an A.

The report says that, for A levels, the A* rules mean “it is possible for a relatively small mark change to move a grade B directly to an A*”.