Ofqual has admitted it made an “early decision” to award grades outside of the normal possible range for foundation and higher-tier GCSE papers, as it believed this was “the fairest thing to do” in the circumstances.

But the admission is likely to raise further questions about Ofqual’s lack of communication, as the grades came as a surprise to schools when they were released last month.

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Appearing before the Commons Education Select Committee this morning, Dr Michelle Meadows, Ofqual’s executive director for strategy, risk and research, was asked: “How were errors including pupils on foundation GCSEs receiving impossibly high standardised grades missed by Ofqual?”

She responded: “We took an early decision with regards to tiering. So tiering is, as you’ll know, for certain subjects where the span of ability of students is really wide and there’s different content to be taught for the most able versus the less able - we have these tiers.

“And normally what happens is that, if a student is entered, for example, into the higher tier and then fails to achieve a grade 3, they fall off; they become ungraded.

“And for a foundation tier there are a small number of students each year who are capped, effectively, so the most they can do is 5. And this is just a product of the fact that they are put into these separate papers.

“In the absence of papers this year, we really felt that the fairest thing to do was to remove those limits on students’ performance.”

It is unclear exactly when this decision was made, but it can be assumed the exams regulator did not inform schools before grades were released - as the leader of one of the country’s largest multi-academy trusts called for an independent inquiry into the issue when he saw his schools’ results.

Sir Jon Coles, chief executive of the United Learning Trust and a former Department for Education senior civil servant, asked why students entered for the foundation tier in some subjects - where the maximum grade is a 5 - were awarded grades of 6 or higher by the algorithm.

Today, Dr Meadows said there were a “very, very small number of cases” in which students achieved grades outside of the possible range for their tier.

“Less than 1 per cent of foundation tier students received higher grades, and for the higher tier, it was less than half a per cent [who] received lower grades than they would normally achieve,” she said.

“But we felt it was actually a decision in favour of students - that they wouldn’t be constrained in the normal way.”

She added: “We simply removed the cap that would be normally there - because that cap is an artificial cap.

“And unfortunately, it’s a very difficult decision for teachers, whether to enter a borderline student for foundation or higher tier. And sometimes in a normal year, unfortunately, it goes wrong. Students do better than expected or worse than expected.

“So we wanted to remove that constraint this year, so that students were able to get higher grades with the standardisation process. And it did happen in a very, very small number of cases.”

Dr Meadows was also asked at what point the Ofqual algorithm “mutated”, as indicated by prime minister Boris Johnson last week.

She said: “I don’t believe the algorithm ever mutated.”