Some results have not yet been double-checked

This year, reading and writing sections were sent to different examiners, as part of a trial marking system.

But there was a delay in getting the marks back and about 170 schools received them after the end of the academic year.

Publication was set for 24 August. No revised date has been given.

'We apologise to schools'

The Qualifications and Curriculum Authority, which regulates exams, said results for tests in maths and science - the other two compulsory national curriculum subjects assessed at age 14 - would still come out on the planned date.

A spokesman said: "There was a delay, which we have already discussed. We apologise to schools for that delay but the important thing from our point of view was to get the results to schools, which we have done."

Last week, the Secondary Heads Association said it expected about 25,000 teenagers to see their English marks increase as a result of efforts to tackle the problems with exams.

Schools have demanded re-marks after complaining of "inconsistent" and "erratic" scores, the association added.

The pupils who took the tests were the first to complete all three years of the government's strategy aimed at boosting achievement between the ages of 11 to 14.

Schools had been due to get their results back in July.

For the first time this year, one examiner handled responses to the reading question, while another dealt with the writing paper.

The change from a single examiner for an entire paper was intended to improve the accuracy of the marks awarded.

Experts believe focusing on marking one answer makes assessments more consistent and reliable.