Only the top three per cent of GCSE students will receive the highest grade in English and Maths when the new exams are sat from 2017 onwards.
Exam regulator Ofqual said this has been introduced in a bid to bring about greater differentiation towards the top end of results, BBC News reports.
Schools will start teaching the new GCSEs in English, English Literature and Maths in 2015, and the current grading system will be replaced by a numerical one - with Grade 9 being the highest, down to Grade 1.
The top three numbers will replace the A and the A*, meaning it will be easier to see who the very best performing students are. It is predicted the same number of students who currently receive As and A*s will be given Grades 7 to 9.
Headteachers have warned that no student should be at a disadvantage because of this new system.
Chief regulator Glenys Stacey said "statistical evidence" will be used to ensure there is a smooth transition and that no pupil will be adversely affected by the change. This will also "provide some certainty about what to expect at this time of significant change".
While the new Grade 4 is expected to be equivalent to a current C, former education secretary Michael Gove insisted he wanted the new-look GCSEs to be tougher than the ones currently being sat.
General secretary of the Association of School and College Leaders Brian Lightman warned that harder exams do not necessarily mean higher standards.
"Excellent teaching and clear leadership are what enable students to achieve more," he told BBC News.
He added it was important for employers to know what grades students had achieved when it came to applying for jobs.
At the moment, Ofqual is accrediting the new GCSEs and the new syllabuses for English and Maths should be delivered to schools before Christmas.
Posted by Alan Douglas