Charity work funded by government is being wasted because the law restricts the ownership of intellectual property, according to the Directory of Social Change.
As the law stands, intellectual property developed with government funding belongs to the Crown. This means charities that carry out projects and research for the state are unable to continue their work without the Government's consent when funding expires.
In a series of policy proposals drawn up for autumn's political party conferences, the DSC will call for intellectual property ownership to be shared.
"Restricting the benefit and usage of developed research by not letting people use it once the funding ends is crazy," said Ben Wittenberg, director of policy and research at the DSC, a training organisation that campaigns for an independent voluntary sector.
"Unless government lets us - at the very minimum - share ownership of what we develop, it's not partnership and we have no choice but to keep asking for more money."
Ann Blackmore, head of campaigns and communication at the NCVO, said each contract should be assessed on its merits. "How intellectual property is managed should be part of the discussion when you enter into contract negotiations," she said.
Tom Fitch, chief executive of Community Accountancy Self-Help, which trains small charities in accountancy and has been funded by public bodies to carry out work, said he agreed with the DSC's position and that work done by charities should remain in the public domain.
An Office of the Third Sector spokesman said that relinquishing intellectual property rights would expose it to the risk of having to pay one charity if it contracted another to continue its work - and this would not be good value for taxpayers' money.