The Government is facing a legal challenge over new legislation for "back to work" schemes which it is accused of "shamefully" rushing through Parliament.
Lawyers announced the move to bring judicial review proceedings as soon as possible after Work and Pensions Secretary Iain Duncan Smith lost an appeal at the UK's highest court against a ruling that earlier regulations underpinning the schemes were invalid.
Five Supreme Court justices upheld a Court of Appeal decision that 2011 regulations were legally flawed, but rejected claims that back to work schemes amounted to forced labour.
Since the Court of Appeal's ruling in February, the Government has fast-tracked new legislation, the Jobseekers (Back to Work Schemes) Act, through Parliament, which validates the 2011 regulations retrospectively.
After the latest decision in the legal battle, Phil Shiner, head of Public Interest Lawyers, said: "Today's ruling from the Supreme Court is of huge constitutional and practical significance. My firm will now get on with challenging, by judicial review, the retrospective legislation which was shamefully rushed through Parliament by Iain Duncan Smith in March of this year."
Responding to today's ruling, Mr Duncan Smith said: "We are very pleased that the Supreme Court today unanimously upheld our right to require those claiming jobseeker's allowance to take part in programmes which will help get them into work.
"We have always said that it was ridiculous to say that our schemes amounted to forced labour, and yet again we have won this argument.
"Ultimately this judgment confirms that it is right that we expect people to take getting into work seriously if they want to claim benefits."
The legal battle over the schemes has centred on claims brought by university graduate Cait Reilly, 24, from Birmingham, who challenged having to work for free at a local Poundland discount store and by 40-year-old unemployed HGV driver Jamieson Wilson, from Nottingham, who objected to doing unpaid work cleaning furniture and as a result was stripped of his jobseeker's allowance for six months.
Critics condemned the schemes as ''slave labour'' because they involved work without pay and cuts in jobseeker's allowance for those who failed to comply with the rules, while those in favour welcomed them as an effective way of getting people into employment.
Supreme Court President Lord Neuberger, Lord Mance, Lord Clarke, Lord Sumption and Lord Toulson dismissed the Secretary of State's appeal on the issue of lawfulness, holding that the 2011 regulations were "invalid" as they did not contain a sufficiently detailed "prescribed description" of the schemes.
But on the issue of whether such schemes amounted to "forced labour", the justices dismissed an appeal by Ms Reilly and Mr Wilson, ruling that the regulations did not constitute forced or compulsory labour.
At the Court of Appeal Lord Justice Pill, Lady Justice Black and Sir Stanley Burnton unanimously agreed that the 2011 "work for your benefits" regulations failed to give the unemployed enough information, especially about the sanctions for refusing jobs under the schemes.
Ms Reilly, who was at the Supreme Court, said: " I am really pleased with today's judgment, which I hope will serve to improve the current system and assist jobseekers who have been unfairly stripped of their benefits.
"I brought these proceedings because I knew that there was something wrong when I was stopped from doing voluntary work in a local museum and instead forced to work for Poundland for free.
"I have been fortunate enough to find work in a supermarket but I know how difficult it can be. It must be time for the Government to rethink its strategy and actually do something constructive to help lift people out of unemployment and poverty."
Giving the unanimous decision of the Supreme Court, Lord Neuberger and Lord Toulson said: "On the facts of the present case, there was a failure to provide either Ms Reilly or Mr Wilson with adequate, accurate information about the schemes in relation to themselves before they were informed that their participation was required."
The justices said the Secretary of State's appeal was "complicated" by the fact that since the Court of Appeal ruling the 2011 regulations had been repealed and replaced by the 2013 regulations and the Jobseekers (Back to Work Schemes) Act 2013 had come into force.
Lords Neuberger and Toulson stated: "This court, like other courts, is normally concerned with stating the law as it is, not as it was.
"Further, it is rather unattractive for the executive to be taking up court time and public money to establish that a regulation is valid, when it has already taken up Parliamentary time to enact legislation which retrospectively validates the regulation."
Jonathan Isaby, political director of the TaxPayers' Alliance said: " This verdict may be embarrassing for the Department for Work and Pensions, but campaigners should not be allowed to exploit it to undermine necessary and fair welfare reform.
"This judgment is about the way ministers introduced legislation into Parliament. It certainly does not reject the concept of mandatory work experience.
"Job seekers should be expected to take any opportunity to get off benefits, even if it isn't their dream job. Programmes like this and Work for the Dole are needed to tackle long term worklessness."
Welcoming the ruling, TUC general secretary Frances O'Grady said: "The Government say they want to make work pay. But this kind of scheme is work with no pay, and employers can use it to replace paid staff with free labour. Sacking paid staff and replacing them with unpaid conscripts is the opposite of making work pay.
"Instead we need policies that create real jobs such as a jobs guarantee for the long-term unemployed and young people.
"Ministers must stop treating hardworking people who lose their jobs through no fault of their own as if they are all potential benefit cheats."