Philip Evans, head of the pound;19,000-a-year Bedford school, said exams did not need radical reform but new grades were needed after "grade inflation".
He said. "You need to be able to distinguish between able candidates, but over the past 15 years there has been such grade inflation it is now difficult to do so. I would have re-graded the examinations. But to avoid comparisons with existing A-levels, you would need to introduce new scores of, say, one to seven, one being an A**, two an A*, three an A and so on."
A quarter of his pupils ditch GCSEs and A-levels in favour of the International Baccalaureate, which gives a more rounded academic programme.
But Dr Evans said there was no enthusiasm in the independent sector for a diploma that fused academic and vocational exams. "I have always recognised the need for academic and vocational qualifications, but they are different things," he said.