England’s largest schools exam board has admitted it made an error in a maths GCSE exam question taken by pupils yesterday.

An exam paper from the board asked, “How many 125 millimetre glasses can be filled from a 2 litre bottle of water?” The question should have read ‘millilitre’ instead of ‘millimetre’.

The question was in a foundation maths GCSE paper taken yesterday. The board insists pupils' results will not be affected by its mistake.

But Paula Goddard, a senior examiner working who has worked for all of England's school exam boards, told TES: “The interesting point now is, how will they mark the exam papers without being unfair to those that attempted it by reading what was supposed to be there, those that answered it as it was written and those that didn't attempt it because they were confused.

“The overall pass mark will have to be lowered for the exam that contained the errors. But this won't solve the issue of where candidates’ stress levels remained higher, due to the finding of the error themselves.”

A spokeswoman for AQA said: “Unfortunately one of the questions included the word ‘millimetre’ instead of ‘millilitre’. Given the context of the question, we think most students will have answered it in the way it was intended but, if any didn’t, our examiners will make sure it doesn’t affect their result.”

The error has sparked outrage on Twitter:

@Just_Maths never mind that question, the confusion that may cause could affect later q's too. Not good! — Katie Baker (@edukatemaths) June 10, 2016