Fashion retailer Zara is under investigation over allegations of slave labour amid claims that workers in its factories in Argentina are working under “degrading” conditions, it is understood.

La Alameda, a workers‘ rights group in the country, claims that it discovered immigrant workers, including children, producing garments for the retailer in sweatshop conditions where they were forced to work more than 13 hour days while having to seek permission to leave the premises.

Labourers were mostly Bolivian, The Daily Mail reported, though the sweatshop was based in Buenos Aires and produced items for the Zara Man collection, available in UK stores.

Juan Gomez Centurion, head of the country‘s health and safety watchdog, explained the conditions in which the workers were found.

“We found men and children who lived in places where they worked,” he commented.

“They were not registered and they were living in terrible conditions. They had no official documents and were held against their will, they were not allowed to leave their workplaces without permission.”

Zara‘s ongoing international expansion is driving profit for its owner fashion retail group Inditex, which last month reported a 22 per cent increase in net profit over its full financial year to €2.3 billion (£2 billion).

Inditex has denied any wrongdoing, commenting: “We are surprised by the allegations.

“Based on the limited information we have received so far, the workshops in question do not appear to have any relationship with our approved suppliers in Argentina.”