More than a million children will get their Sats results late because of administrative chaos, the Government admitted yesterday.

Children's Secretary Ed Balls said that more time is needed to complete the marking of papers for 11 and 14-year-olds and to 'resolve technical issues'.

Results for Key Stage Two are expected to be received by schools a week late on July 15, and for Key Stage Three by the end of that week.

The tests for 11-year-olds are seen as the most crucial as they determine primary schools' ranking in official Government league tables.

Schools Secretary Ed Balls has ordered an enquiry into the marking delay as more than a million children may not find out their results before the end of term

The data is also passed to secondary schools, enabling teachers to decide how to group new arrivals in key subjects if they use setting. An independent inquiry into the reason for the delay has begun and will report to the qualifications regulator Ofqual.

The watchdog has already accused the National Assessment Agency, which oversees the testing, of letting teachers and pupils down.

The marking shambles is an embarrassment for the Government and has prompted teaching unions to demand that Sats tests are scrapped.

Teachers assessing the papers have been warning for months of administrative problems at ETS Europe, the firm handling the marking for the first time on behalf of the NAA.

Senior examiners have also claimed that quality control is weaker this year, so pupils may receive less accurate results.

The Times Educational Supplement yesterday revealed that marking of Key Stage Two English and Key Stage Three reading and maths was continuing into the weekend.

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This is despite the fact that all the test papers were due back in primary and secondary schools by Tuesday. The problems are believed to be worst in English.

Dr John Dunford, general secretary of the Association of School and College Leaders, said that 14-year-old tests should be 'downgraded to an internal check on student progress in future'.

He said: 'This is further evidence that the high-stakes testing regime in England has become too extensive and unmanageable.'

Liberal Democrat schools spokesman David Laws said the marking had been a 'complete and utter shambles'. He said: 'The Government and the Educational Testing Service have failed on the most basic test of all  -  to mark papers in a timely and reliable way.

'It is frankly scandalous that there has been this degree of incompetence in marking tests which are considered by the Government to be of such importance to schools. Teachers and children deserve much better.'

Kathleen Tattersall, chairman of Ofqual, said the findings of the inquiry would be published later this year. She said: 'Pupils and teachers work hard throughout the year and it is unacceptable that they have been let down in this way.'

In a letter to the Commons' schools select committee, Mr Balls said the delay was unsatisfactory and 'clearly unacceptable'.

A spokesman for the NAA said: 'This is a serious failure by ETS Europe for which we apologise to schools, pupils and parents.'