Sainsbury’s supermarket has vowed to terminate contracts with any suppliers that breach employment law. A spokeswoman said Sainsbury’s had launched an investigation into recent allegations made in The Guardian about some of its suppliers. She said: “While we do not employ these workers directly, we take this issue extremely seriously.

“We have worked very closely with all our suppliers to ensure that they are aware of the potential issues surrounding temporary labour.

“Sainsbury’s is a responsible employer and would terminate all contracts with any supplier proved to have seriously breached the law.”

Sainsbury’s supplier Grampian Foods said that all employment agencies it used were checked and audited to ensure they complied with legislation. The firm has launched its own investigation.