The federal mandate transformed a voluntary expense into a compulsory one, increasing demand exponentially.

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Drug company and medical trade associations also demand that their members conform to voluntary codes of conduct.

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"While more popular voluntary schemes in the environment and children's education are oversubscribed, less in-demand areas like hospitals, prisons and GPs' surgeries could really benefit from volunteers to complement staff", he said.

BBC: NEWS | UK | Public volunteers at record level