The Suffolk boarding school, where children can choose whether or not to attend lessons, has been given six months to improve standards or be closed down by the Department for Education.

But Baroness Blatch, known for her uncompromising right-wing stance when an education minister, told the House of Lords that parents have a right to choose to send their children to the school.

If parents wanted to pay for their children to study at the school, which has a philosophy at variance with the government's approach to education, they should be allowed to do so, she said.

Liberal principles

The independent school, founded on liberal principles of free expression for pupils, has exam results above the average for state schools and very high levels of support from parents and pupils, said Baroness Blatch.

Other former ministers also condemned the closure threat, which followed a damning report from the Office for Standards in Education into the school.

Lord Glenamara - who as Ted Short served as education secretary under Harold Wilson - described the threat against Summerhill as an "outrage" and backed the right of schools to be different.

"Please don't try to iron all schools out in accordance with Mr Woodhead's ideas," he told the House of Lords, calling on them to support the "splendid old school".

Former Conservative minister, Baroness Young, described the school as "pioneering" and that its experimental approach had contributed much to mainstream education. Any attempts to shut the school would "damage the whole educational system".

Speaking for the government, Lord Hunt said that inspectors had found "serious weaknesses" in the school and that it was legitimate for Ofsted to want to see improvements in standards.

The school, founded in 1921 by AS Neill, has the aim of encouraging pupils to be confident and independent, helping them to "create a happier childhood by removing fear and coercion by adults".

Attendance at lessons is not always obligatory and pupils are allowed a considerable degree of self-determination in how they study and live.