Of the 670 affected candidates, from schools in Central, Kowloon, Tai Po and Yuen Long, 248 had their overall score downgraded. For the rest, the oral score was affected.

At least two students' scores dropped below the 14 points required for them to study in their own school and two fell below the minimum eight points for any Form Six study. At least four students failed the oral test because of the error.

At 7pm yesterday, the bureau had contacted most of the affected students and about 100 of them said they had no problem in finding a Form Six place.

But exam authority and Education and Manpower Bureau chiefs were unable to say how many students had missed out on places at English-medium schools or other preferred schools.

Irving Koo Yee-yin, chairman of the Hong Kong Examinations Assessment Authority, said: 'We apologise. We are asking the Education and Manpower Bureau to set up a special taskforce to proactively contact them with a view to helping them. The promise from us and from the bureau is that no students affected by this incident will be disadvantaged in their entrance to Form Six.'

Mr Koo said fees for appeals over affected candidates' papers would be waived after one student demanded to know why he should have to pay $675 for checking a revised grade that he did not trust.

The exam authority discovered the error on Wednesday while investigating a student's appeal against a grade in the English syllabus B.

Authority secretary-general Peter Hill said the error occurred when a supervisor failed to apply a computer programme module used for combining the grades of papers that had been through dual marking to one of the exam papers.

Dr Hill said the supervisor in question and the head of the information systems services division had resigned yesterday morning.

Secretary for Education and Manpower Arthur Li Kwok-cheung said he was extremely concerned about the incident and vowed to work towards a satisfactory outcome for the affected students, mostly from the New Territories.

'I can give a guarantee that no students as a result of this mistake would be affected in terms of their matriculation of getting into Form Six, and I can also give a guarantee that we will do our very, very best to ensure that they would be given the choice of their school,' Professor Li said.

He also expressed regrets about the blunder but insisted the HKEAA had swiftly informed the bureau of the mistake once it was confirmed.

'I have asked the authority to account for the incident and review the information system as well as the results processing procedures. This is to ensure that there will be no recurrence.'

The Office of the Ombudsman yesterday announced that it had already requested information from the HKEAA so that it could consider whether a direct investigation into the case was warranted.

Wrong answers

Number of students affected by the error:

670 in Kowloon, Central, Tai Po and Yuen Long

Entire English syllabus B score is downgraded for 248 candidates, score of oral part for 422

223 eligible for Form Six admission are affected

Two candidates did not meet minimum eight-point requirement for admission to Form Six due to downgrading

Two candidates did not meet 14-point requirement for entering Form Six at their own or a linked school