The proposals from the Qualifications and Curriculum Authority would see GCSEs brought into closer alignment with A-levels, which have been modular since 2000.

Pupils would be able to complete up to half of their GCSEs before the end of their courses, and they could re-sit individual modules or "unit" exams to get better grades.

The proposals emerged as about 630,000 pupils wait to receive their GCSE results this week.

Alan Smithers, Professor of Education at the University of Buckingham, urged caution over moves to break GCSEs into "bite sized" units.

"The breaking up of the course can mean that pupils may not have an integrated understanding of the subject," he said. "Modularising the GCSE is likely to increase overall results. This is partly because it will be easier for the individuals to perform at a higher level through the restructuring of the exam."

But there will also be people who choose to re-sit their units "to maximise their score".

"This is something that the pupils themselves see as unfair. The re-taking of units - even once - introduces an element of unfairness."

A QCA consultation paper on the proposed reforms to GCSEs said: "Unitisation in GCSEs can enhance flexibility and choice."

Currently, most GCSEs are assessed through external exams taking place after two years of study. The reforms, which would come into force in 2009, would not necessarily apply across all GCSE subjects, or to all exam boards.