Differentiation in the U.K. egg market continues apace, with retailer Marks and Spencer now selling boxes of six free-range double-yolk eggs.

Six medium free range own brand eggs sell at the U.K.’s largest retailer Tesco for GBP1 (US$1.54), however, the double-yolked Marks and Spencer offering will retail at GBP2.75 per box.

They are part of a new range which includes Araucona Blue and Maran Island brown eggs, and have grabbed multiple column inches in the U.K. press since being launched.

According to the British Egg Industry Council, double yolks occur only in 0.1 percent of eggs. The retailer is guaranteeing, via candling, that all eggs will have double yolks.

Marks and Spencer product developer Ali Rodham, commented: “We’re really excited to be selling the double-yolkers. We think they’re cracking and we’re sure our customers will too. Perfect for people who think the yolk is the best bit of the egg.”