The Colombian blacktail hen eggs are all from one farm that supplies the supermarkets. Daily Mail reports that free-range birds from one flock wandered on to a field being used for clay pigeon shooting and ate lead shot.

After some of the chickens became ill, a vet was called. Lead suspicions arose when he discovered that the birds had higher than normal levels of lead.

The eggs, which apparently make up 1% of Waitrose's organic egg supply, were removed from the shelves.

"As a precaution we are recalling extra large, large and medium organic blacktail Colombian organic eggs with the code of OUK 20137 stamped on each individual egg. This recall applies to all date codes up to and including May 21," said a company spokesman.