Morrisons said it would take the matter up with CP urgently. "We are concerned by the findings of the investigation. Our ethical trading policy forbids the use of forced labour by suppliers and their suppliers.
A Tesco spokesperson said: "We regard slavery as completely unacceptable. We are working with CP Foods to ensure the supply chain is slavery-free, and are also working in partnership with the International Labour Organisation [ILO] and Ethical Trading Initiative to achieve broader change across the Thai fishing industry.