Private schools are being warned they could lose their charitable status unless they do more to help their less privileged neighbours.
Eton College has a rowing lake which it shares with other schools
A new Charity Act will require independent schools to show they are meeting a public benefit test.
Heads will be warned of the dangers of losing their charitable status at a conference organised by Brighton College on Wednesday.
They will also consider whether their charitable status is still justified.
'New public benefit test'
Robert Maas, tax partner of Blackstone Franks LLP, is telling delegates: "I am here because one of the big advantages of being a charity is the exemption from tax."
"I am sure you will not be surprised to hear that if a charity loses its charitable status the Revenue will want to claw back the tax relief that has previously been given to the extent that the funds have not been used for charitable purposes.
"Although the advancement of education is still a charitable objective, it will have to be positively shown that a school meets a new public benefit test for it to be recognised as a charity."
Many independent schools already assist neighbouring state schools.
For example, Eton College has a 2,000 metre international-standard rowing lake for shared use with other schools, colleges and community groups.
Cheltenham Ladies' College allows maintained schools use of its ICT facilities at no charge and pupils at Malvern College, Worcestershire run French and German language clubs for local school children.
But such schemes will have to become more widespread when the new Charity Act comes into effect.
Helping specialist schools
Sir Cyril Taylor, chairman of the Specialist Schools Trust, will urge independent school heads at the conference to sponsor new city academies and specialist schools.
"We want to build upon what is already happening - there are a whole raft of ways of doing this," Sir Cyril told BBC News Online.
"Everybody should be concerned if there are children in underperforming schools. It's everybody's responsibility to help change that.
"We want to see an inclusive education sector."
The Education Secretary, Charles Clarke, is also due to address the conference.
Anthony Seldon, the head of Brighton College, said the gap which had existed between the state and independent sector was closing.
"What has become clear is that the damaging educational apartheid that has existed in this country for 100 years, where neither sector really engages with the other, is coming to an end and I am full of hope that having the education secretary address independent heads will usher in a new age of co-operation," he said.