Outraged headteachers in the North-East have joined the row over claims that examiners may have deliberately manipulated A-level grades.

Hundreds of high-flying students across the country failed their A-level course work modules despite receiving top grades in their exams.

Headteachers fear the grades have been altered to head-off accusations that A-levels are getting easier.

One student at Yarm School, in Teesside, received an unclassified mark in her A-level psychology course work, but 100 per cent in both the exams she sat.

The school was so concerned it sent 14 psychology papers back for remarking to exam board OCR after several students failed the course work.

Headteacher David Dunn said: "We are very angry. These are conscientious pupils who got grade As in their other modules. "I am certain that these results are being manipulated at the 11th hour for political reasons. "There is such an erosion of confidence in the exam system that nobody knows what they can believe."

Yarm School's head of psychology, Jo Nixon, who has taught the same course work for seven years, said she was distraught when the results came through last month.

"It's incomprehensible that they would get unclassified, no teacher would let course work go through unclassified because they are allowed to work at it and improve it," she said.

At Ampleforth College, near York, there have been similar queries over English AS level course work as well as course work in A-level history and English.

Father Leo Chamberlain, the school's headteacher said: "It is a matter of great concern to us and we are making our protests through the HMC."

The Headmasters' and Headmistresses Conference (HMC), which represents independent headteachers, said it was waiting for heads to pursue their complaints, but said it would back them if they wanted to take legal action.

The exam board OCR insisted it had followed the rules and said it was meeting with heads to discuss their concerns.

Yesterday Liberal Democrat Education Spokesman and Harrogate MP Phil Willis demanded an independent inquiry into the grade-fixing allegations, saying the Government had to prove itself ''beyond reproach''.

A spokeswoman for the Department for Education said the exams watchdog, the Qualifications and Curriculum Authority was investigating complaints.

''It is utter rubbish to suggest that the Department instructed the QCA or OCR to downgrade exam papers," she said.