It doesn't work. It replaces real jobs. It is an invitation to abuse and fraud. It is used as a punishment for being unemployed. It is (probably) illegal.
Companies and charities using workfare placements should be sued for minimum wage, distress and costs.
Recompense ideally should be from the companies involved although with our corrupt establishment selected legal system no doubt it is the UK taxpayer will pick up the bill. We will have to pay the benefits for the employees losing their jobs because of the workfare scheme anyway and at least the cash will go to the deserving instead of the scrounging rich.