Thousands of GCSE and A-Level exam papers could have been marked incorrectly last summer, according to a whistleblower.
Channel 4 News said David Leitch, a senior supervisor at OCR(Oxford Cambridge and RSA Examination), found wrongly calculated final scores in papers that schools had referred for checking.
He said a wider search uncovered more mistakes but claimed he was instructed to inform only schools which had requested paid-for remarking.
Dissatisfied with a review ordered by regulator Ofqual, C4 News reported, he emailed 30 schools directly to alert them to errors and has now been suspended by OCR pending a full inquiry.
Speaking to the programme, he said: "We checked 50,000 scripts and found 700 errors...I believe there would have been thousands. Not thousands of incorrect grades, but thousands of incorrect results issued. What I found with the incorrect results that I uncovered, was that about 10% of them were incorrect results that should be a higher grade, 10% were results that should have been a lower grade and 80% were no grade change."
Mr Leitch said after he spotted the mistakes he was told by OCR to stop the checks. He then became concerned that regulator Ofqual was not going to force OCR to carry out the checks.
Mr Leitch told Channel 4 News: "It became apparent to me that they were almost siding with OCR. They seemed to be saying the same things that OCR were saying, that the candidates had not authorised these checks to be undertaken which I thought was strange.
"Why would a candidate need to give authorisation for us to add up the marks on the script, find out they're wrong, and then we give them a fair mark for what they've achieved."
Stephen Twigg MP, Labour's Shadow Education Secretary said: "These allegations are extremely serious. I will be writing to OCR and to the regulator, Ofqual, to ensure that there is a thorough investigation. Parents, pupils and schools need confidence that the exam system is rigorous and fair."
Graham Stuart, Chair of the Education Select Committee said: "If an awarding body knew that a significant number of entrants had received the wrong grade but did nothing to put it right for a lot of those pupils, then it was guilty of a serious breach of faith. That is the allegation and, given its source, it needs urgent investigation to find out the truth."