Labour shadow ministers have accused exam regulators of using an "unlawful" system to work out students' A-level grades.
Grades were first assigned last week by exams regulator Ofqual, using an algorithm that moderated the results that teachers had predicted for students, based on previous grades and their school's performance in recent years.
But thousands of students, many of whom were from disadvantaged backgrounds, found themselves with much worse grades than expected. After days of public outrage from across the political spectrum and student protests, results went back to grades predicted by teachers on Monday.
But Labour Shadow Attorney General Lord Falconer of Thoroton has argued that the system itself was unlawful on at least three counts, in a joint letter with Shadow Education Secretary Kate Green addressed to Education Secretary Gavin Williamson and Ofqual boss Sally Collier.
The letter says: “If the system involves in essence no more than the teachers putting their students in order and then an algorithm assigning grades to the students based principally on the grades students in previous years in that institution achieved, it does not accurately reflect that student’s level of knowledge skill and understanding.
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“Ofqual acknowledge this is what they have done by expressly accepting that CAG (centre-assessed grades) is secondary to standardisation.
“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.”
It 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.”
It comes after Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), demanded that Education Secretary Gavin Williamson launch a review into the results process to rebuild trust after the fiasco left “public confidence... badly shaken”.
He said: “It seems to be clear that the statistical model for moderating centre-assessed grades was flawed and that it produced many anomalous results.
"But how did this happen, why were the problems not foreseen, and why were ministers not on top of this? Most importantly, what lessons can we learn for the future?
Mr Barton's call for a review comes after the Office for Statistics Regulation (OSR) and the Commons Education Select Committee both launched investigations into what went wrong with this year’s exam results.
The OSR said its review will consider to what extent Ofqual's system was in line with the UK's statistics code of practice, but will not look at individual results or make a judgement on how to award grades without exams.
Robert Halfon, chairman of the education committee, called the situation an “absolute disgrace” and said his panel will launch an inquiry after MPs come back from the summer recess.
He told Times Radio: “We need to also ask very deep questions as well as to whether Ofqual is fit for purpose in its current role, or whether it needs to be completely integrated into the department so you know for sure who is behind the decision making.”
Mr Williamson said that Ofqual “didn’t deliver” the right grading system despite the Government being “reassured” it would be in place.
Mr Williamson has apologised to students but has repeatedly refused to say if he will resign.
New polling figures show backing for the Conservative party has dropped markedly in the past week, when the results chaos took place.
YouGov found that found that public support for the Conservatives dropped from 44 per cent to 40 per cent in just a week.
The Tories' slide happened as backing for Labour rose from 35 per cent to 38 per cent over the same period, the poll claimed.