... nine Year Six pupils out of 90 were able to complete a complex maths question normally answered by only the brightest students in the country. Despite the difficulty of the question, none of the children, aged ten or 11, had written down any of their workings-out.

There was also a dramatic drop in the number of questions answered by pupils when an inspector sat in on the test compared with the previous day.

And investigators found a bundle of maths test papers that had been opened ahead of an exam.