Lucy Powell has demanded ministers apologise for the “disruption and chaos” caused by the online publication of answers to this year’s SATs exams for seven-year-olds.

She has also asked Education Secretary Nicky Morgan to clarify why the department is “failing to deliver on the basics” of education following the first real terms drop in budgets for 20 years, class sizes growing and teacher shortages in a letter sent this afternoon.

The answers to the Key Stage Two spelling and grammar tests were published on a secure website for four hours yesterday ahead of the tests, which took place today despite the leak. The Conservatives blamed this on a “rogue marker” but Powell said it was the responsibility of the Government to ensure integrity in the exam system and demanded the Government launch an urgent inquiry.

This follows another embarrassment for the Department of Education when they were forced to cancel the key stage one test after the questions were leaked in April.

Powell, shadow Education Secretary, said the Government had caused “chaos” and brought about a drop in parents’ confidence in state education.

“There is now no confidence left among parents, teachers and school leaders in this year’s primary assessments, as a result of your Department’s incessant chopping and changing and failure to deliver a smooth transition of reforms. There is also widespread concern that the tests as they stand do not correlate to the preparation that many children have done.

“It was reported this weekend that up to 1,000 primary schools could be forced to become academies on the basis of Key Stage 2 assessments. With the results of the tests today entirely compromised, for the Government to use them as a device to hold schools to account would be wholly unfair and wrong

“A robust assessment regime needs consistency and to be understood by all. This Government has utterly failed to deliver this, and the children and parents who have been let down every step of the way deserve an explanation.”

SATs are standardised tests designed to measure a child’s progress as well as how well they are being taught. They are compulsory in state primary schools, and usually are taken at age seven (key stage one) and eleven (key stage two).

This follows a “parents’ strike” last week, in which parents kept children home for the day to protest over-testing of their primary school children. It is not known how many kept children home but over 40,000 signed a petition campaigning against excessive assessment or under-11s.

Since the start of this academic year the Department for Education has published, updated or clarified on average at least one primary assessment document or resource on average every other working day.

The Government attempted to extend their reforms by forcing all state schools to become academies, but u-turned on the policy after it attracted widespread criticism from Labour as well as some Conservative MPs.

Christine Blower, general secretary of the National Union of Teachers, said the mismanagement of SATs was the end to a “dismal year” for primary school children.

“After months of confusion and mismanagement, they mark the dismal culmination of a dreadful year for primary pupils and their teachers. They constitute an experience which must never be repeated; those who have engineered it must be held to account.