Sir Mike Tomlinson, who led a review of exams for ministers, was among those criticising the plans this week. He also said that universities would increasingly favour the International Baccalaureate exam as A-levels were not properly assessing students' ability to think for themselves.
Under the A-level changes, which ministers want to introduce for courses beginning in 2008, students would be able to achieve up to a grade A on compulsory questions. They would then have to choose whether to take a harder section of the exam, likely to be based on longer essay questions and testing overall understanding of the subject. Those doing well would get a merit or distinction.
The plan aims to address universities' complaints that they cannot choose between thousands of pupils with strings of A grades.
But critics, including the Qualifications and Curriculum Authority, the Government's exam watchdog, say that the harder questions should be compulsory. They worry that some schools will not teach students how to answer the optional section. This means universities will not be able to use the results from that section when selecting students, as it would be unfair to applicants who have not been given the chance to do it.
Sir Mike, a QCA board member, said it had never favoured the optional approach. "There's an equity issue. I don't think it's acceptable." Geoff Parks, director of admissions for the Cambridge colleges, said: "Our view is that (questions) have to be compulsory - that is the only way to guarantee equality of opportunity."
Martin Ward, deputy general secretary of the Association of School and College Leaders, warned inner-city pupils might lose out, as their schools might not be able to offer them the support of those in more prosperous areas.
But the Government believes that making the questions mandatory would mean an A grade would be devalued. In a letter to Ken Boston, QCA chief executive, in February, Ruth Kelly, then education secretary, wrote of introducing compulsory questions: "We would be extremely concerned about the impact such an approach would have on the existing A-level standard."