This report from the Alliance to Save our Antibiotics argues that while UK supermarkets are making progress in their responsible antibiotic use policies, they should expand them to cover all animal products that they sell. While all the leading supermarkets have antibiotic policies in place already, they usually only cover own-brand animal products.
Marks & Spencer and Iceland were the only supermarkets studied that apply their antibiotic policies to all their animal product suppliers. The policies of ASDA, Aldi, Lidl, Morrisons and Tesco do not clearly cover all of their own-brand produce, in some cases only applying to UK-sourced raw meat, fresh eggs and fresh milk.
Only M&S, Tesco and Waitrose publish comprehensive data on antibiotic use in their supply chains. There is very little data - across most supermarkets - on the level of antibiotic use by farming system (e.g. intensive, free range, organic or pasture-fed).
Read the full report, Resistance & Responsibility: Antibiotic use in supermarket supply chains, here (PDF link). See also the TABLE explainer What is the connection between infectious diseases in humans and livestock?