Supermarket giant Sainsbury's has hit back at criticisms that the poultry meat and eggs on sale in its stores are derived from systems which involve animal suffering.

Thousands of letters and leaflets have been sent to its customers across the country this week, stating that it only sources these products from farms demonstrating high levels of animal welfare.

"We take our responsibilities for animal welfare very seriously as we know that, for our customers, it is not only the quality of what we sell that is important, but also how these products are sourced."

All of Sainsbury's chicken and eggs are from British farms, it says, though they are sourced from a range of production systems.

Two accompanying leaflets explain the different labels that appear on their products, with a basic interpretation of what they mean.

For example, Sainsbury's basics eggs are from caged hens, though they all carry the British Lion Quality mark to show they are from quality assured units.

Its basics chicken all carry the Red Tractor quality assurance logo, showing it has been produced to high welfare standards.

Sainsbury's adds that it plans to end all egg sales from caged birds from 2010.

These have criticised the UK poultry industry and in particular the supermarkets' role in demanding cheap products, forcing producers into intensive production systems

Celebrity chef Hugh Fearnley-Wittingstall's programme, Hugh's Chicken Run, was especially critical of the big multiple retailers for perpetuating what he sees as cruel systems of broiler production.

Jamie Oliver's Jamie's Fowl Dinners, to be shown on Friday, is expected to make similar claims about supermarket egg procurement.