Ofqual boss Glenys Stacey admitted today she would have forced one of England's biggest exam boards to alter its GCSE English boundaries to avoid grade inflation.
The regulator has the power to direct grade boundary changes and would have done so if Edexcel had not revised them, she suggested.
The disclosure came as new figures showed that at least 143 secondary schools are set to fall below the Government's floor target for pupils achieving at least five Cs including English and maths as a result of the GCSE English fiasco - putting them at risk of being considered failing.
Leaked letters published today showed that Ofqual pressurised Edexcel to alter its GCSE English grade boundaries just two weeks before results were published last month.
Appearing before the Commons education select committee today, Ms Stacey was asked what Ofqual would have done if Edexcel had stuck to its first response to the regulator, and insisted that its proposed grade boundaries were fair.
“If they had done so, then the legislation provides that the regulator can direct grade boundary changes,” Ms Stacey said.
Pushed on whether Ofqual would have done this, she added: “I think we would have done, yes.”
The leaked correspondence, seen by the Times Educational Supplement (TES) show that Ofqual wrote to Edexcel on August 7 amid concerns that there would be a rise in C grades, calling on them to act quickly to produce results that were closer to predictions for the subject.
The board responded a day later, saying it believed its proposed grade awards were “fair” and there was no justification for further changes.
It added that Ofqual still wanted an alteration, that the board could move the minimum requirement for a C grade for one of the English units up to 65 marks out of 96 - 10 marks higher than in January when it stood at 55.
Ofqual replied on August 9, with a letter from Mr Opposs that stated Edexcel is obliged to ensure its results are consistent with other awarding bodies, whose results were close enough to predictions.
Alex Cunningham, Labour MP for Stockton North, asked Ms Stacey why Edexcel had changed its mind, saying “was it the fact that you adopted a strong-arm tactic to tell them 'you must ensure that these grades are downgraded'?”
Ms Stacey replied: “What changed was, that we knew, looking at that, that there would be a six or seven per cent increase, grade inflation, that we did not think to be right or justifiable.
”We therefore wrote to Edexcel pointing out that they needed to bring the qualification in appropriately. They reflected on that and it's quite right and proper that they should have done.
“The way the system is set up, in the legislation that we all operate to, requires us to put that challenge back to them. It then requires them to look at whether they can justify their outcomes and that's what they did.”
The Association of School and College Leaders (ASCL) raised concerns today about the numbers of schools which have seen their overall GCSE results drop due to the English grading crisis.
This year secondary schools fall below the Government's floor target if they fail to have at least 40 per cent of their pupils getting at least five Cs, including English and maths, and less than the national average of pupils making two levels of progress.
ASCL said that a survey of its members had found that 143 schools said, in the wake of the grading fiasco, their results had gone down, taking them below the target when they had expected to be above it.
In total, 730 schools had responded, with 641 saying that their results had been lower than expected this year. Of these, around 500 had said the main reason for this was GCSE English.
Speaking after the select committee, ASCL deputy general secretary Malcolm Trobe said: “There's a huge risk as soon as you enter the position of falling below the floor target.”
These schools could be converted into academies, he said, and there could be “a significant risk to jobs, not only to the headteacher but other members of the leadership team”.
Mike Griffiths, head of Northampton School for Boys, told the select committee that hundreds of headteachers, like him, had seen their students “hopes and dreams really shattered” by the fiasco.
“My belief as a headteacher is that Ofqual has simply failed to maintain standards.”
Ms Stacey also told the cross-party group of MPs that English was a particularly difficult subject to set standards for and there was a “large element of judgment” involved in marking the exams.
She told MPs Ofqual wrote to not only Edexcel but also the WJEC exam board after their preliminary results were too generous.
“Edexcel - the preliminary results were high,” she told the committee. “If the provisional results had been left to stand I think we were looking at 6 per cent or 7 per cent inflation and I suspect there would have been a different outcry had that been the outcome.
”They were certainly out of line with the other awarding body results.“
She added: ”There was a clear recognition that this really did need a challenge.“
Amanda Spielman, who chairs Ofqual, told the committee she was surprised how high the grade predictions were at some schools.
”You might have thought that this year, in the first year of a completely different exam, schools would be a bit more cautious about their predictions and have brought them down a bit,“ she said.
”I'm not saying it is the schools' fault, I'm saying school expectations were in a very different place. We would have expected in the face of a new specification to see schools being more cautious and what we actually saw was that school expectations for Cs went up by 2 per cent."
Ms Stacey told the committee that if January's grade boundaries had been applied to June's students, there would have been grade inflation of five or six per cent.
"What we have seen so far, and we have nothing to doubt it, and don't expect to doubt it, is that the June boundary setting occurred properly," she said.
"That does, as I say, leave us all in a very uncomfortable position, and we have thought carefully about fairness, and we keep on thinking about it. We do think the right thing to do is to offer a re-sit opportunity to those students."
In a written submission to MPs ahead of today's evidence session, Ofqual also said that nobody could have seen that January's results were too generous, and that all the evidence pointed towards decisions being harsh.
And it insisted that there has been no political interference in the exams.
An Edexcel spokeswoman said: "We have been consistent in stating that grade boundaries for Edexcel GCSE English this year were the subject of lengthy discussion both with Ofqual and the other awarding organisations.
"With the introduction of new specifications, all awarding organisations needed to make changes to their January boundaries for June to ensure standards were maintained year on year. We also considered reissuing grades for students who took units in January."
She said that at the time the leaked letters were issued, other exams boards had already made decisions over their grade boundaries, and had them accepted by Ofqual.
"Given the relatively small number of students who take English with Edexcel, the grade boundary decisions of other awarding organisations have a larger impact on national results than our own.
"We felt that the original grade boundary changes suggested by Ofqual, based on prediction data and the decisions of other awarding organisations, would not enable us to adequately reflect student work in their grades.
"After extensive discussion with Ofqual, we agreed a June grade boundary which took account of our concerns to recognise the candidate performance our examiners observed. This reported results slightly above original Ofqual predictions.
"We are therefore satisfied that the final grade boundary we set for June enabled us to fairly reward learners as well as uphold the standard of the GCSE."
A WJEC spokesman said: "We find ourselves in a difficult and unexpected position, which has implications for all our candidates in England and Wales.
"In the summer we acted on joint instructions from regulators to adjust our GCSE English language awards downwards at Grade C, in order to ensure comparable outcomes.
"We now find one regulator confirming that the decision made was correct, and another asking us to re-grade, reversing the previous joint decision.
"As an urgent next step, we have asked the regulators to explore the possibility of agreeing a common view so that we can act to remove the uncertainty for schools and colleges in England and Wales, and ensure a coherent and rational way forward for all our candidates."
The Commons education select committee will take evidence from Education Secretary Michael Gove tomorrow.
Ofqual also announced today that it has ordered the OCR exam board to take action after it found a number of clerical errors in the marking of the summer 2011 exams.
Ms Stacey said: "The number of clerical errors made by OCR examiners when adding up candidates' marks in the summer of 2011 was simply not acceptable.
"OCR did not have adequate arrangements in place to check for such errors. When the problems came to light, senior managers did not take control of the situation to identify the full scope of what had happened, or make sure all the results were right."
Ofqual's investigation found that of the 100,000 scripts checked, 1,370 contained clerical errors which resulted in changes to 251 unit or qualification grades. A number of scripts were destroyed and could not be checked.
OCR chief Mark Dawe said: "I am deeply saddened and disappointed that these clerical errors were made during my first year in post. Some of the legacy operational systems were clearly in need of revision and Ofqual's direction is helping me to carry out a wider-ranging reform of our systems, practices and procedures.
"I would like to reassure teachers and students that the improved processes and systems we already have in place are delivering the highest level of clerical accuracy."