Following a number of high-profile mistakes in recent exam papers, qualifications watchdog Ofqual is demanding that tests are checked more rigorously.
The organisation has written to exam boards demanding that papers face additional checks.
Ofqual chief executive Glenys Stacey said: "The recent run of exam errors are disappointing and unacceptable. While the vast majority of question papers taken so far have been free from error, there have been a number of question papers that have included errors. We take instances like this very seriously."
She added that awarding organisations must take steps to protect students from further disruption and anxiety.
Around one million candidates are due to sit GCSE, AS-level and A-level exams this summer.
However, thousands of AS-level students have been left stumped in recent months after coming across several unanswerable questions.
More than 40,000 students were affected when a question in a business studies exam contained incorrect figures.
Posted by Katy Kearns