The pupils studied the wrong play

It is understood the examination authority, the Council for the Curriculum, Examinations and Assessment (CCEA), informed Regent House about the change.

However, due to changes in staff the information was missed.

Meanwhile, the CCEA has confirmed that 70 pupils at Cookstown High School in County Tyrone were affected by a similar mistake.

There the play, Pygmalion, was taught on the GCSE English Literature course, when it was in fact on the Drama syllabus.

The CCEA said pupils at both Regent House and Cookstown High will not be penalised.

In a statement the exams council said the students' papers would be judged on their poetry and prose answers.

A CCEA spokesman added that hundreds of thousands of examinations were carried out successfully every year.

"Where things go wrong for whatever reason, we work closely with the schools or colleges involved to ensure no candidate is disadvantaged," he said.

"We will ensure each pupil affected by this incident gets a fair deal."

'Special consideration'

The CCEA said it wanted the candidates to know that their marks for the two sections of the paper they were able to complete would be rounded up to a full mark for the paper.

It was an error that should not have occurred and we will be looking at our procedures to make sure that nothing like this happens again

Principal David Thompson

"In addition, if candidates have suffered because of stress and disruption, they are eligible to apply for special consideration," he said.

Regent House principal David Thompson said there had been a "slip up".

The school is one of the province's largest grammar schools with almost 1,500 pupils.

Mr Thompson told the Belfast Telegraph: "It is embarrassing for the school. CCEA have been very supportive and have indicated that there is no question of the youngsters being penalised."

Mr Thompson said the pupils "seemed to be as content as one could be in this situation".

"It was an error that should not have occurred and we will be looking at our procedures to make sure that nothing like this happens again," he said.