More than 100 voluntary sector organisations made use of jobseekers who were told to carry out work placements without being paid or face losing their benefits, government documents show.
The names of more than 500 organisations that provided the controversial placements between July 2011 and January 2012 have been released by the the Department for Work and Pensions.
The department, which had sought to keep the information under wraps, has been told by the Court of Appeal to publish the information after a lengthy legal battle.
The list names dozens of well-known charities, including the British Heart Foundation, Cancer Research UK, the National Trust, Save the Children, Oxfam and the RSPCA, plus scores of smaller voluntary sector organisations including hospices and animal charities.
Many charities, including Scope, Sue Ryder, Age UK, the BHF and CRUK, pulled out of providing the placements by early 2013 after pressure from the campaign group Boycott Workfare.
Under the scheme, which was referred to as mandatory work activity and was scrapped last year, thousands of jobseekers were told to work for free for 30 hours a week or face losing their weekly benefit payments.
The DWP had argued that revealing the names of the organisations would harm their commercial interests but were told by the Court of Appeal to reveal the names after a battle lasting four years.