The Government was warned that cancelling exams and opting for calculated grades for students amid the Covid-19 pandemic would be the “worst-case scenario”, the Ofqual chair has suggested.

Roger Taylor, chairman of the exams regulator, said ministers decided to abandon GCSE and A-level exams after Ofqual suggested running socially-distanced exams or delaying tests, before cancelling them.

He told MPs that it was a “fundamental mistake” to believe Ofqual’s algorithm for awarding grades “would ever be acceptable to the public”.

His comments come amid continued anger about the handling of grading GCSE and A-level exams which were cancelled during the coronavirus crisis.

Ofqual’s controversial algorithm for awarding calculated grades had appeared to boost private schools’ performance and led to many other A-level students having their results downgraded following moderation.

But addressing the Education Select Committee, Mr Taylor insisted that the standardisation process “reduced the advantage enjoyed by private schools”.

Although he recognised the level of fairness “was not felt to be acceptable”.

Ministers and government departments, including Number 10, were repeatedly warned by Ofqual of the risks of the system, MPs heard.

Mr Taylor told MPs that Ofqual’s initial advice to the Secretary of State in March was to try and hold the summer exams in a “socially-distanced manner”, with the second option being to delay exams.

He said: “The third option – if neither of these were acceptable – would be to have to try and look at some form of calculated grade.

“We did also look at whether that might be a teacher certificate rather than attempting to replicate exam grades.

“That was our advice to ministers.

“It was the Secretary of State who then subsequently took the decision and announced without further consultation with Ofqual that exams were to be cancelled and the system of calculated grades were to be implemented.”

He said that opting for the third option of calculated grades was the “worst-case scenario”, adding that it was a “political decision”.

Julie Swan, Ofqual’s executive director for general qualifications, said they met with the schools minister “on a weekly basis” throughout the process.

She said: “When we first gave our advice on the options on March 16 – which was written for ministers – we did say it would be challenging, if not impossible, to attempt to moderate estimates in a way that is fair for all this year’s students. Everyone I think throughout the process was aware of the risks.”

Ms Swan said an Ofqual paper highlighting “the risk to public confidence” and “widespread dissatisfaction” was sent to the General Public Sector Ministerial Implementation Group in May.

She said Number 10 was also briefed by Ofqual on August 7 about the risks to “outlier students”, schools who expected improved grades and the impact on low entry cohorts, including private schools.

When asked about the issue at Prime Minister’s Questions, Boris Johnson – who previously blamed the debacle on a “mutant algorithm” – said Ofqual made it “absolutely clear time and again” that the system was robust.

Committee member Ian Mearns, Labour MP for Gateshead, asked the watchdog during the hearing: “At what point did the algorithm mutate?”

The decision to use a system of statistical standardised teacher assessments was taken by the Secretary of State and issued as a direction to Ofqual

Dr Michelle Meadows, executive director for strategy, risk and research at Ofqual, responded: “I don’t believe the algorithm ever mutated.”

Sally Collier resigned from her role as head of Ofqual last week, while the Department for Education (DfE) announced that permanent secretary Jonathan Slater would be standing down a day later.

In a written statement to the Education Committee ahead of the hearing, Mr Taylor said: “Understandably, there is now a desire to attribute blame.

“The decision to use a system of statistical standardised teacher assessments was taken by the Secretary of State and issued as a direction to Ofqual.”

He told MPs that Ofqual advised Education Secretary Gavin Williamson against changing the appeals process to include mock exam results but the minister announced the policy anyway.

Mr Taylor added: “Our advice was that this was an extremely risky thing to do because we were very unclear about how it could be delivered in a way that was consistent with Ofqual’s legal duty.”

Tory MP Robert Halfon, chairman of the committee, summarised Ofqual’s defence as “not me guv”.

He questioned why Ofqual did not use the time between receiving schools’ grades in June and results day in August to test the algorithm “rather than wait until the eleventh hour” to find anomalies.

Mr Halfon asked: “Should you have done your own mock exam in terms of the algorithm?”

Responding to the concerns, Dr Meadows told MPs: “We tested the model thoroughly.

“We were confident that the model that we chose was the most accurate overall and the most accurate for those different groups of students.”