England's exam regulator Ofqual has launched an official inquiry into blunders in this summer's GCSE and A-level papers that affected up to 100,000 students.
The inquiry, to be carried out with Ofqual's fellow regulators in Northern Ireland and Wales, aims to discover exactly how the mistakes found their way into the exams and "hold the awarding organisations to account".
Pupils sitting the crucial tests were faced with apparently impossible questions in some cases because of an error in the paper.
Sandra Burslem, deputy chairwoman of Ofqual, said: "We have made it clear that the errors on exam papers this summer are unacceptable.
"Ofqual's priorities during the exam season were to make sure the awarding organisations did everything possible to prevent further errors and to make sure that, where errors have occurred, the marking of papers neither unfairly advantages or disadvantages the candidates involved.
"Now that the taking of exams is over we turn our attention to an inquiry. This will hold the awarding organisations to account for their mistakes by finding out the root causes of the errors and what needs to be done to put things right. The regulators will not hesitate to take regulatory action as necessary at any stage to protect the interests of students."
A total of 10 mistakes - two printing errors, and eight problems with the questions themselves - are being investigated by Ofqual, in partnership with CCEA in Northern Ireland and DfES in Wales.
Ofqual said that about 100,000 candidates would have been faced with the mistakes, which included a multiple choice question featuring four wrong answers in an Edexcel AS-level biology paper sat by 17,000 students
The inquiry, which could lead to regulatory action, is being held with the intention that such mistakes never happen again. It will also look at how exam bodies communicated with pupils and their schools, and how they could improve their procedures. A report into the matter is due to be published by the end of the year, once the inquiry is complete.
The exam regulators are monitoring the actions of the awarding organisations to make sure the students affected do not suffer any unfair disadvantages or advantages. Some pupils have raised concerns that their grades, and in turn university places, could be affected.