Private schools could have to share facilities with local schools to demonstrate they are fulfilling their charitable obligations under guidelines issued on Wednesday.

Legislation coming into force in March will for the first time require more than 11,000 independent schools with a charitable status to show their aims are for the public benefit.

Critics of private education have long protested that independent schools should not enjoy tax breaks under charitable status when their high fees excluded all but the most wealthy.

Previously charities set up to advance education were presumed to have aims that benefited the public and were not required to demonstrate this further.

But this was changed under the Charities Act 2006, bringing independent schools in line with other charitable organisations.

Suzi Leather, chair of the Charity Commission that regulates the sector, said most charities had nothing to fear from the new requirements.

"There is a two-way relationship between charities and society - registered charities enjoy considerable benefits in terms of their reputation and the tax advantages that go with their status," she said.

"In return, they should publicly account for what they do to benefit society, including people in poverty."

The commission published guidelines on Wednesday explaining how it would assess a charity's public benefit.

More detailed guidelines for educational charities will be published later after a consultation starting next month.

In the past the commission has suggested independent schools could demonstrate public benefit by offering bursaries, assisted places or sharing teachers with local schools.

A spokeswoman for the commission said there was no prescribed level of public benefit, but said it had to be more than a token gesture.

"Opening up your playing fields once a year to the local school clearly is not sufficient," she said.

The commission can remove the trustees of a charity that fails to meet its requirements, although it says it prefers to work with them to resolve any problems.