Examiners should be allowed to "blow the whistle" if they have concerns about how the exam system is being managed, head teachers say.

Three head teachers' organisations say that the removal of a confidentiality clause in examiners' contracts could avoid a repeat of the disputes over this year's A-level grades.

It is vital that the work being undertaken by Tomlinson consigns to history the disasters of this year

Edward Gould, HMC chairman

The heads, from the state and independent sector, also want to see restrictions on the executives of exam boards to stop them making changes to exam grade boundaries.

It was a move by the OCR exam board that led to thousands of students having some of their A and AS-level units downgraded.

After concerns were highlighted, the Education Secretary, Estelle Morris, ordered an independent inquiry which led to nearly 2,000 students having their results upgraded.

The Headmasters' and Headmistresses' Conference, the Girls' School Association and the Secondary Heads Association were presenting their arguments on Monday to the head of the independent inquiry Mike Tomlinson, as he prepares to publish the second part of his review next month.

A and AS-level split

The three organisations are also calling for the two parts of the new Curriculum 2000 A-levels - AS-levels and A2s - to be split, to further reduce the chance of a repeat of this year's problems.

Currently, marks for the two parts are combined to give a final grade.

But when candidates did better than expected in the first phase, at least one board this year raised the standard expected in the second.

The heads say the whole system of marking and grading has become far too complex and opaque and every effort must be made to make the system more transparent.

And they want the exams watchdog - the Qualifications and Curriculum Authority - to become independent of the Department for Education.

The awarding bodies, in turn, should be "demonstrably independent" of the QCA.

HMC chairman Edward Gould said: "For the confidence of future generations of students, parents, universities and employers, it is vital that the work being undertaken by Tomlinson consigns to history the disasters of this year."

President of the GSA Carole Evans said it was crucial that A and AS-level standards were now properly defined.

SHA general secretary John Dunford added: "It is of the greatest urgency that Tomlinson produces a clear definition of the standards of both AS and A2, in order that students and their teachers know what they are aiming for in the 2003 examinations."