Attorney General Dominic Grieve has asked a tribunal to review the rules on whether private schools can be charities.
Independent schools want a judicial review of the Charity Commission’s rules, after two schools were refused charitable status last year.
Mr Grieve has asked the Charities Tribunal, which covers England and Wales, to clarify the law.
Schools say the “public benefit” they must prove is too narrowly defined.
The loss of charitable status threatens tax benefits for independent schools.
The Independent Schools Council, which represents 1,260 schools across the UK, argues that the Charity Commission puts too much emphasis on the provision of bursaries for poorer students in its definition of public benefit.
The Charities Tribunal operates primarily as an ombudsman in specific disputes between charities and the Commission, which also covers England and Wales.
But for the first time, Mr Grieve has asked it to review the interpretation of the law more generally.
In a document, he has laid out various scenarios – in which fictional schools offer provisions such as teaching support and access to sports facilities for local state schools – for the tribunal judges to consider.
In his letter to the tribunal, Mr Grieve said there was “uncertainty” in the operation of the law.
“The uncertainty is contrary to the interests of charity because it means that the charities concerned do not know whether or not they are operating within or without the terms of their constitutions,” the letter said.
ISC chief executive David Lyscom said the organisation was “delighted” with Mr Grieve’s decision.
“The entire sector continues to be at the whim of the Commission’s prevailing and subjective view as to what public benefit means, and what is ‘sufficient’ for a school to pass the public benefit test,” he said.
He said ISC would also continue its push for a judicial review of the issue.
The Charities Commission said the referral to the tribunal was the “appropriate” way to proceed, and Mr Grieve’s reference covered “substantially the same ground as the judicial review”.
“In preparing all our guidance on public benefit, the Commission was at all times diligent in consulting charities and others affected, and in making clear the process we had followed,” it said.
“We stand by our approach and the legal analysis which underpins it, and we are confident that the Commission has acted reasonably and followed due process,” it added.
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