Sainsbury's has admitted it had to sell eggs from caged hens over Christmas after snow hampered supply.

The situation is embarrassing for the retailer, which has only sold eggs from non-caged hens since early last year.

"Due to extreme weather conditions just before Christmas, our suppliers were unable to reach the farms that supply our free-range eggs," said a spokeswoman. "To guarantee a supply of eggs, we decided to take a single delivery of eggs from caged hens."

The eggs were clearly labelled and were only on sale from 24 to 27 December, she added. They were removed once the free-range supply resumed.

The situation underlines the difficulty of ensuring higher-welfare egg supply. Defra secretary Hilary Benn this week denied the government was wavering over the 2012 battery ban, saying it was lobbying the EC for penalties on member states that missed the deadline.