The chlorine washing of food, the controversial "cleaning" technique used by many US poultry producers who want access to the British market post-Brexit, does not remove contaminants, a new study has found.

The investigation, by a team of microbiologists from Southampton University and published in the US journal mBio, found that bacilli such as listeria and salmonella remain completely active after chlorine washing. The process merely makes it impossible to culture them in the lab, giving the false impression that the chlorine washing has been effective.

Apart from a few voluntary codes, the American poultry industry is unregulated compared with that in the EU, allowing for flocks to be kept in far greater densities and leading to a much higher incidence of infection. While chicken farmers in the EU manage contamination through higher welfare standards, smaller flock densities and inoculation, chlorine washing is routinely used in the US right at the end of the process, after slaughter, to clean carcasses. This latest study indicates it simply doesn't work.