The workers were found in a house in Fleury-la-Riviere, in the Marne area of France, with 12 people crammed into dormitory-style bedrooms designed for four.

While there is no evidence that the immigrants had been directly hired by any Champagne house or growers, or that any Champagne producers were aware of the lodging conditions, it is suspected the immigrants were recruited by an agency to work the harvest, which got underway this month.

A criminal inquiry has been opened by the public prosecutor based in Chalon-en-Champagne, Christian de Rocquigny de Fayel. It is expected to last at least two weeks before publishing any results or announcing any prosecutions.

‘I can not make any comment while the inquiry is ongoing,’ Rocquigny de Fayel told Decanter.com, ‘but we are taking this as a serious case of human rights’ abuse. The workers were being kept in extremely exploitative conditions’.

Over 100 of the workers were immediately treated by the local Croix Rouge (Red Cross), while others were rehoused in the neighbouring commune of Damery, or in lodgings provided by local winemakers. Others were sent home to Poland.

The police enquiry will be looking at exactly who was aware of the treatment of the workers, and whether they had legal permits for working in France or whether the agency was sub-contracting the workers to vineyard owners who were happy to work ‘in the black’, so to avoid paying social charges and other taxes.

A spokesperson for the Comite Champagne could not be immediately contacted for comment on Thursday morning.

A spokesperson for the Champagne growers' union, SGV, said that it was considering joining the criminal investigation as a civil party. It was considering 'bringing a civil action for damages to the image of the Champagne appellation', it said.