Whole Foods has chosen its new London store to launch the world's most transparent animal welfare labelling system.

The store's meat and poultry labels carry a welfare rating between one and five, where one is the minimum and five is the highest standard. The higher the rating, the more the product costs.

"Farmers are business people. They're competitive and will want to raise their welfare rating. The higher their rating, the more they can charge for their products; that's what can drive it," said John Mackey, co-founder and CEO of Whole Foods.

Under the rating system - which includes standards on criteria including stocking density and feed - a 'one' is the minimum a farm must achieve to get listed at the retailer. Level two requires a higher degree of transparency in the way the farm is run; level three requires animals to be reared on a pasture-based system; level four forbids any mutilations, such as castration and tail docking; and level five means animals are slaughtered on-farm to minimise their stress.

Ahead of the opening of Whole Foods' Kensington store, buyers had already managed to source British lamb, chicken, beef and pork accredited to level four welfare standards. Duck and veal is rated three on the scale.

Mackey said the scheme would be extended to the US once the infrastructure was in place and high-welfare suppliers established.

Whole Foods is also working on a set of welfare standards for fish and seafood. "The same issues of welfare and environmental sustainability that haunt livestock production are true for aquaculture. Whole Foods is not doing enough in this area," Mackey admitted.

Mackey, a vegan, also launched an attack on the low welfare standards in the organic movement and said the best way of improving the sustainability of meat and fish production was to eat less. "It may not be good for growing retailers, but it's true," he said.