Pupils sat GCSE exam with the answers printed on the back of the paper

The music exam scripts were sent to a number of schools ahead of this summer's GCSE examinations.

The papers went to schools in the Herefordshire and Worcestershire area.

It is believed that pupils sat the exams, set by the Oxford, Cambridge and RSA Examinations (OCR) exam board,  before the mistake was noticed.

Mistake: Answers to GCSE exam questions were written on the back of the papers

An OCR spokeswoman said: "OCR regrets that a printing error may have affected a small number of marks on the GCSE music question paper.

"We are putting procedures in place to identify the effect, if any, this had on candidates and to make allowances accordingly to ensure that no candidate is disadvantaged."

A spokesman for the Qualification and Curriculum Authority (QCA) said the examinations regulator Ofqual would now be checking with the OCR to ensure that "appropriate measures were put in place".

An OCR spokeswoman added that it was not believed that the pupils affected by the glitch would have to resit the exam.

A spokeswoman for the National Confederation of Parent Teacher Associations (NCPTA) said the mishap raised questions about the future of privatised exam boards.

She said: "Every year we have mistakes made by examining boards, mistakes which seriously undermine the hard work done by our students.

"Every year we are told it will never happen again but still it goes on; no doubt before the end of the exam cycle there will be more.

"It must be time now to seriously look at how the privatisation of the examination boards is working, or not as the case may be.

"Is it time for an end to individual boards when a simple thing like proof reading and print checking cannot be achieved?

"How secure do we feel as parents and students that our young people are being given a fair chance?

"Would a central government run system be better, or is the government track record on losing and mislaying document worse? And is this why the exam boards continue to get away with a poor service?"

Last month the OCR caused controversy after announcing plans that would allow teenagers to re-take individual GCSE units to boost their grades.

The OCR exam board published plans for 43 "flexible" GCSEs arguing that modular courses will be less stressful for teenagers than the current "all or nothing" assessments.

But critics of the radical proposals warned that giving schools the option to teach modular GCSEs would make the courses easier  to pass and could give pupils a false sense of their own abilities.