In 1988 a junior health minister, Edwina Currie, made the statement “Most of our [UK] egg production is infected with Salmonella”. The boycott of eggs and egg products by British consumers that followed almost destroyed the British egg producing industry.
In March 1989 new Salmonella legislation was announced:
Zoonoses Order 1989 - Legislation on Compulsory Slaughter and Mandatory Reporting of Positive Results of Tests for Salmonella:
In the following 4 years little improvement was seen in the incidence of Salmonella infections in poultry flocks.
In 1993 the Salmonella legislation was changed. The Poultry Breeding Flocks and Hatcheries Order 1993 was introduced. This order was confined to breeding stock. After 1993 the Salmonella situation began to improve.
Salmonella legislation is supported by codes of practice (COP). These are advisory and are not legal requirements.
The following COP support Salmonella legislation in the UK:

Nobilis Salenvac was used for the initial vaccination of the Lion flock. Vaccination of breeders began in 1994 and vaccination of commercial layers in 1997.