The Qualifications and Curriculum Authority is trialling double-marking to see how effective it would be. Double-marking was carried out on 200 AS biology papers this term.

If the trial proves successful, the practice could be extended to other subjects, though the QCA says it would not be possible for several years.

Ken Boston, the authority’s chief executive, has advocated double-marking ever since he arrived from Australia, where it is widespread, in 2002.

A report last week for the authority said that although the management of the exams system in England was the best in the world, there was some imprecision in measuring grades.

Any disparities between the grades awarded by the two markers would be investigated.

The results of the AS biology trial, involving 16 examiners working on scripts from this summer’s exams, will not be released until the new year.

If the trial proves a success, the next step would be to extend it to a large subject such as English, where an element of subjectivity in examiners’ judgements is inevitable.

The biggest problem facing any large-scale adoption of double-marking is that it is likely to increase the demand for examiners still further.

More than 60,000 teachers mark GCSE, A-level and vocational qualifications and finding extra markers would be difficult.

However, the QCA believes that increasing the use of on-line marking will reduce the demands on examiners and make double-marking of some scripts a possibility.

A possible variation on double-marking all scripts is to re-mark a proportion of each examiner’s scripts so that the boards can judge the quality of their marking.