The findings challenge the popular view that increasing pass rates in public examinations are the result of easier papers.

Researchers concluded that GCSE syllabuses and exams in geography, French, religious studies and physical education from 1996 were at least as demanding as their O level and CSE equivalents in 1976.

Similar conclusions were made about A levels in history, physics, German, and government and politics.

The research was carried out by subject experts and published by the Qualifications and Curriculum Authority (QCA).

Skills required have changed

The exercise is part of a "rolling programme" which aims to ensure that exam standards are maintained from year to year.

The next study will be published later this year. It will focus on German, history and physics at GCSE, and biology, classical subjects, French and psychology at A level.

The Chairman of the QCA, Sir William Stubbs, welcomed the report.

"This work on consistency of standards over the last 20 years helps QCA ensure future standards are maintained," he said.

The report's key findings are:

• Geography at O level/CSE and GCSE Syllabuses and assessment schemes in 1996 were more demanding than those from 1976.

• French at O level/CSE and GCSE The skills required have changed. In 1976, writing was the most important skill; in 1996, listening, writing, reading and speaking were equally weighted.

• Physical education at O level/CSE and GCSE Limited evidence from examination scripts showed that grades were in line with expected standards in both years.

• Religious studies at O level/CSE and GCSE Demands on pupils increased significantly between 1976 and 1996.

• A level history Changes in syllabuses and examinations did not make the syllabuses or exams any less demanding.

• A level physicsThe amount of recall and mathematical knowledge tested was reduced, while the importance attached to understanding and the ability to apply knowledge increased. Overall, these changes did not make syllabuses and exams any less demanding.

• A level German Grade A scripts were of similar standard across boards and over time, but there were concerns about the standard at grade E.

• A level government and politics No significant change in the demands made on pupils or the standards expected at each grade.