Private and state school headteachers have called for the examination system to be updated.

Anthony Seldon, headmaster of Brighton College, said the independent sector should devise its own, broader curriculum for sixth formers by adopting some parts of the international baccalaureate.

Welcoming the idea, John Dunford, general secretary of the Secondary Heads Association, said all schools should unite to force the examination system towards the diploma proposed by Sir Mike Tomlinson, former chief inspector of schools, which has been rejected by the education secretary, Ruth Kelly.

"If we can't have it by the front door, let's have it by the back door," Dunford said.