'The prime minister must now take personal responsibility for this crisis by addressing the country in the next 24 hours to explain precisely how he will end this historic injustice, ' she said on Twitter.
The algorithm, used after exams were called off due to the coronavirus pandemic, has now been abandoned after widespread outrage since A-level results were released on Thursday.
Barrister Jo Maugham said his Good Law Project had appointed solicitors to pursue litigation on behalf of students, and urged the government to launch a suitable appeals system in time for students to go to college in September.
The Department for Education said a cap on the number of places that universities can offer was being lifted.
The backlash over exam results adds to the criticism facing Mr Johnson over his handling of the pandemic and on education, with ministers under fire over plans to get schools reopened full-time in September.
Ofqual has confirmed CAG will be awarded to students for A-levels, AS-Levels and GCSEs, furthering that students who received higher moderated grades could keep that grade over their CAG.
This morning, the government did not rule out the prospect of a Scottish-style U-turn which would see grades based on teacher assessments rather than an algorithm.
The central British government's decision, which applies to England, mirrors those made by devolved governments in Wales and Northern Ireland on Monday, and in Scotland last week.
"This is not the actions of a body that seems to know what it is doing", he told Sky News.
The DfE said it is continuing to work with Ofqual to build as much "fairness into the appeals process as possible" to help what it described as the "most hard cases".
"Ofqual continues to consider how to best deliver the appeals process to give schools and pupils the clarity they need", a DfE spokesman said in a statement issued late on Sunday. Exams regulator Ofqual said some of the predicted grades given by teachers were "implausibly high".
In a further setback for the Education Secretary, the Daily Telegraph reported that some members of the Ofqual board now wanted to ditch the algorithm.
The government's U-turn follows last week's announcement from Scotland's Education Secretary John Swinney, who revealed thousands of students would have their exam results upgraded following public anger at low grades.
Of the 295,000 pupils at Dubai's private schools, 109,894 attend United Kingdom curriculum schools, making it the most popular curriculum in the emirate.
Students hold placards as they take part in a protest march from Codsall Community High School to the constituency office of Gavin Williamson, Conservative MP for South Staffordshire and Britain's current Education Secretary, in Codsall near Wolverhampton, central England on 17 August 2020, to demonstrate against the downgrading of A-level results.