During the late 1980s there was a sharp increase in the occurrence of Salmonella enteritidis phage type 4 in the UK and Europe.  Investigations implicated poultry as a source of this strain of salmonella, and poultry meat and eggs as food vehicles.

Since 1998, when the new Lion Code of Practice was introduced, the number of Salmonella food poisoning cases in humans has fallen dramatically and is now two-thirds of the 1980s level.  The fall has been attributed by Government to poultry vaccination, an integral part of the Lion Code of Practice.  In 2004 a survey by the Food Standards Agency found no salmonella in 28,000 British eggs tested.

However, several other European countries have experienced continued outbreaks of salmonella and there have been outbreaks among humans in the UK directly linked to imported eggs.  Tests by the Health Protection Agency (HPA) on imported eggs in 2004 found nearly 7% tested positive for salmonella.  In the same investigation, salmonella was not recovered from any British Lion eggs. The HPA issued a further warning in October 2004.

The status of UK egg production as among the safest in the world was confirmed in a report by the European Food Safety Authority published in 2007.  Several EU countries reported levels of salmonella of public health significance on their flock holdings of more than 50%, while the UK figure was only 8%.  The vaccination programme stipulated in the Lion Code of Practice ensures additional protection against salmonella for British Lion eggs.