The doomed algorithm used by Ofqual which downgraded thousands of A-level results was unlawful, Labour has claimed.
Shadow attorney general Lord Falconer is arguing that both ministers and the exams regulator would have been aware that the algorithm was in breach of the law at least three times.
At least 40% of A-level results were downgraded from what teachers had predicted by a standardisation formula which assigned grades to students partially based on their previous attainment and on grades achieved by previous years at their school or college.
It meant A-level results day was blighted for students across the country who had been expecting grades their teachers had predicted for them, after the coronavirus crisis meant they could not sit their exams.
The government stood by what Boris Johnson said were "robust" results before it performed a U-turn, allowing students to use the grades their teachers predicted for them.
Lord Falconer said the standardisation formula used to calculate grades was in breach of the objectives under which Ofqual was established in 2009.
In a joint letter with shadow education secretary Kate Green, addressed to Education Secretary Gavin Williamson and chief regulator of Ofqual Sally Collier, Lord Falconer said the algorithm "does not accurately reflect that student’s level of knowledge skill and understanding".
“This is clearly not in compliance with objective one, and therefore cannot allow for a proper comparison with other boards or years, because there is no proper assessment of this years’ students.”
According to the law which established Ofqual - the Apprenticeships, Skills, Children and Learning Act 2009 - the regulator must "secure that regulated qualifications give a reliable indication of knowledge, skills and understanding".
The letter continues: “Separately it is inherently unfair not to have any right of appeal against the grade awarded, beyond errors of application in the system.
“They should have the right to complain they were wrongly graded on the merits. The decision is so important to their life chances. That is a second unlawfulness.
“There will be a mass of discriminatory impacts by operating the process on the basis of reflecting the previous years’ results from their institutions.
“It is bound to disadvantage a whole range of groups with protected characteristics, in breach of a range of anti-discrimination legislation. That is a third unlawfulness.”
Earlier the Department for Education said it had "full confidence" in exams regulator Ofqual, despite Education Secretary Williamson on Tuesday appearing to shift blame for the A-levels results fiasco onto the watchdog.
Mr Williamson on Tuesday said Ofqual "didn't deliver" after hundreds of thousands of A-level students were left disappointed by their results, which were downgraded by an algorithm.
But ahead of GCSE results day on Thursday, the DfE said: "We have full confidence in Ofqual and its leadership in their role as independent regulator and we continue to work closely with Ofqual to deliver fair results for our young people at this unprecedented time."
It added: "Our focus remains on working with Ofqual to ensure students receive their final GCSE, AS level and A-level results this week so that they can move on to the next stage of their lives.”