Asda launched a campaign last month to force its supermarket rivals to only source British eggs, after Somerfield announced that it would import 40% of its free-range eggs from France.

The retailer attacked 12 supermarkets, calling them the “dirty dozen”, in an attempt to pressurise them into committing to sourcing only British eggs.

Hannah Naseem, Asda egg buyer, said: “It’s a disgrace that the dirty dozen are prepared to turn their backs on British free-range eggs and opt for cheap imports. We’re calling on them to follow our lead and commit to only buying British free-range eggs instead of getting them from countries that don’t carry the Lion mark of quality.”

According to Asda, the “dirty dozen” includes Tesco, Sainsbury’s, Morrisons, Somerfield, Iceland, Aldi, Lidl, Netto, Budgens, Co-op, Spar and Kwiksave.

John Widdowson, vice-chairman of the British Free Range Egg Producers Association, said: “We want to see all retailers supporting British free-range egg producers. There needs to be a much closer relationship between farmers and retailers to ensure foreign free-range eggs are no longer imported to the UK. There is no reason why British farmers can’t supply all of the free-range eggs consumers want to buy – but they need supermarkets to invest here in the UK, not abroad.”