It just doesn't add up. England's exams regulator has told boards to re-write their new maths GCSE exams after finding that three of the four had made their papers too hard.

And regulator Ofqual said the fourth exam board, AQA, had been ordered to make its papers "more challenging". Pearson - which owns Edexcel - OCR and WJEC Eduqas had made then exams too hard, said Ofqual.

The move comes after Ofqual analysed the results of 4,000 mock tests for GCSEs due to be studied in schools from September 2015.

The government, and especially Michael Gove, the former Secretary of State for Education, had demanded that the exam boards draw up new, rigorous maths and English GCSEs.

Ofqual determined that OCR, Pearson and WJEC Eduqas exams failed "to differentiate effectively across the full range of ability. This is due to the assessments being too difficult."

The regulator added: "Even the students from the best performing schools scored poorly. The evidence suggests that if these assessments were live exams, they would not function well."

Chief exams regulator Glenys Stacey was reported by the BBC as saying: "What we are doing here is an unprecedented amount of analysis. This is not going back to the drawing board. This is going to happen in the next few days. This is not a substantial re-write by any means, it's making sure standards are right in a sufficient and even-handed way."