The first of a new breed of GCSEs that give students a choice of vocational and academic options within each subject are expected to be launched next year.
In the most radical change to the structure of the exam since it began in 1988, all GCSEs are likely to become entirely modular by 2010, Ken Boston, the exams regulator, has revealed.
The reform is designed to give students more options as they progress through courses and aims to prevent them being pigeonholed as either vocationally or academically orientated at 14.
It will also establish a structure which will form the backbone of a possible English diploma, which may supersede GCSEs and A-levels within 10 years.
Last year, Dr Boston, chief executive of the Qualifications and Curriculum Authority, argued in The TES that the GCSE needed sorting out.
Some exams are not modular, while others are. GCSEs in various subjects have different numbers of "tiers" tailored to students' range of ability.
The current system places 14-year-olds on vocational or academic pathways from which it is often difficult to escape.
But the reformed GCSE will be a modular or unit-based qualification. Each student will sit a series of compulsory or "general" units in subjects including English, maths, science and computing.
They will then be given a choice of specialist units in either vocational or academic areas for each of those subjects. These modules will be put together to create the GCSE in that subject.
Dr Boston believes pilots of the new-style qualification in some subjects could begin next year, with the first of the new exams taken in 2007. All subjects would be modular by 2010.
The architecture of the new GCSE fits in with plans put forward by a government task force on the future of 14-19 education, which is recommending the introduction of a diploma system by 2014.
The plan for a diploma envisages pupils studying a compulsory core of communication, functional maths and computing. They would then complete optional courses and aim to build up enough credit to obtain a diploma.
Dr Boston believes the proposed changes will mean that the structure and content of GCSE courses could be transferred to the diploma system.
The task force, led by the former chief inspector Mike Tomlinson, has put forward proposals for a four-tier, all-embracing diploma system to replace GCSEs, A-levels and vocational qualifications.
But the plans have yet to be costed and ministers will not decidewhether to accept them until the autumn at the earliest. Dr Boston's GCSE proposals would also need ministerial approval.
But Alan Smithers, professor of education at Liverpool university, said that the increasing emphasis on individual units meant that pupils would have to be tested on each unit.
This would not meet ministers' goals of cutting the assessment burden, unless some units were not examined. But this could make the qualification less trusted by the public.
"It seems to me this is a move in the wrong direction," he said.