A leading independent school has declared it will stop teaching A-levels unless they are made more rigorous.
Barnaby Lenon believes the new exams would be tougher
Barnaby Lenon, head teacher at Harrow School in London, said too many pupils were getting top grades and coursework made the system vulnerable to cheats.
He said the school would switch to the new "Pre-U" qualification - an alternative to A-levels for students aiming for top universities.
It is currently being developed and is due to be taught from 2008.
The exam would involve studying three subjects over two years, with final exams and an extended essay, rather than the modules of A-levels.
The University of Cambridge International Examinations (CIE) has developed the Pre-U - first announced last October - in response to demand from teachers wanting to prepare students for higher education more effectively.
Writing in the school's magazine, the Harrow Record, Mr Lenon said: "If the A-level system is weakened rather than strengthened in the next few years we will move to the Cambridge board Pre-University exams which start in 2008 as an alternative to A-levels.
"They will combine the flexibility of A-levels with the promise of harder questions and reliable examining."
The new qualification involves pupils sitting final exams after two years
He said that AS and A-level examiners made too many mistakes when marking scripts.
A-levels had not been dumbed down across the board - history questions, for example, had changed little in 30 years, he said.
"The main reason for the improved A-level grades is not that questions have got easier but that pupils are allowed to sit parts of the A-level (modules) at different stages of the course and they are allowed to re-sit modules in order to improve grades."
In some subjects, questions are less challenging than in the past as exam boards try to make courses like maths and French more popular, he said.
Earlier this year, Dr Anthony Seldon, head of Wellington College, another independent school, called for a review of GCSEs and A-levels, saying confidence in the exams was at an all-time low.
The government has said it will reform A-levels to stretch candidates more and help universities and employers choose between the best students.
The department of education defended the A-level as being "a tried, tested and trusted qualification".
But it said it was looking to make changes including introducing tougher questions, an extended project and providing universities with A-level unit grades.