The ban, which represents a welfare improvement for hundreds of millions of hens, looks like it will not be adhered to in up to 13 EU states come 1 January. While Compassion in World Farming will be celebrating a major step forward in animal welfare on New Year’s Day, the charity is calling on both individual countries and the European Commission to act immediately to enforce the ban, which was first voted for back in 1999.

Compassion's Director of Public Affairs, Joyce D'Silva, said: "It is scandalous that there are still countries who have ignored this impending deadline, despite it having been agreed 12 years ago. We call on the European Commission to prosecute those found breaking the new law."

It makes sound business sense for farmers to switch from these cages to a non-cage system altogether – as the market for free-range eggs continues to grow. In the UK alone, the market for free-range eggs is growing about three per cent each year.

In the UK, the threat of illegal eggs entering the supply chain has also caused concerns. Marketing regulations mean it is illegal to sell eggs from hens in these cages come 1 January but Compassion fears liquid eggs could be used in products, such as pasta, cakes and ready meals which are then shipped to this country.

"We're concerned that consumers could unwittingly buy illegal eggs in the New Year, if the enforcement of the ban is not robust," said Ms d'Silva, "We'd urge consumers to guard against this by checking that the eggs in the products they are buying are free-range."

UK egg farmers are expected to comply with the ban and Compassion is asking them to use this opportunity to move to cage-free egg production, rather than to the so-called 'enriched' cage system, which is permitted under the new rules.

Compassion supporters are currently writing to Agriculture Ministers across Europe, urging them to keep the welfare of millions of hens in mind when they meet in Brussels on 15 to 16 December, a meeting which may be the last chance to agree a common position on the these illegally produced eggs before the ban comes into place on 1 January 2012.