Most of the UK’s biggest supermarket chains are falling short on measures to reduce the use of antibiotics in the production of the meat and animal products they sell, campaigners have warned, with potentially harmful impacts on human health.

Lidl performed worst of the nine supermarket chains examined by the Alliance to Save Our Antibiotics, a pressure group made up of several NGOs.

Lidl had no publicly available policy on the use of antibiotics in its farm supply chain, leaving consumers in the dark and with no publicly available evidence of any effort to curb the overuse of antibiotics of concern.

The supermarket told the Guardian it had been working on a policy, which would soon be published. The policy it sent to the Guardian is four sentences long and “encourages producers to optimise welfare, health, hygiene, husbandry and biosecurity” of their animals, using antibiotics “as little as possible and as much as necessary”, without containing any specifics on how this can be achieved or measured.

The overuse of antibiotics on farms is a major cause of the growing resistance in humans that is giving rise to superbugs, bacteria impervious to all but the strongest medicines and which pose a huge and growing threat to human health.

The UK’s chief medical officer has repeatedly warned that growing resistance to antibiotics could render even routine operations highly dangerous in a few years.

The best-performing supermarket was Waitrose, which not only has a clearly articulated policy on antibiotics in its supply chain, but also a strategy for reducing antibiotic use and a commitment to publishing the results, showing the amount of antibiotics used on the farms from which it is supplied.

The supermarket also bans the routine use of antibiotics on its farms, and the use of some of the strongest antibiotics, which the World Health Organisation has urged should be reserved for the use of human patients, not farm animals.

Marks & Spencer, Sainsbury’s and Tesco were ranked next, while second from bottom were Asda and Aldi, which had publicly available policies on antibiotic use but few stringent measures associated with them, with the Co-op group also falling short on measures such as banning the strong antibiotic colistin and publishing data on antibiotic use.

Suzi Shingler, campaign manager at the Alliance to Save Our Antibiotics, said: “These findings show some supermarkets are finally starting to take the issue of antibiotic resistance more seriously. This is very welcome and has undoubtedly contributed to the recent reductions in use.

“Unfortunately, our survey also shows that some supermarkets have much more to do, and others have yet to take any significant action.”

All of the supermarkets in the report were contacted by the Guardian for comment. Some referred the Guardian to the British Retail Consortium, which represents major retailers. Andrew Opie, director of food policy at the trade body, said in a statement: “Retailers are aware of the challenges in relation to continued use of antimicrobials in the supply chain and advocate that medicines are used responsibly.

“This prevents unnecessary use while protecting against any negative effects on animal welfare. It is important that any decisions are supported by robust scientific justification. Significant reductions have already been achieved in UK food and farming and retailers are working collaboratively with industry partners to make sustained improvements.”

A herd of Friesian dairy cows feeding in a cattle shed. Photograph: Alamy

In addition, Asda said it would soon update its antibiotics policy.

Waitrose said: “Waitrose recognises the potential risks to human healthcare of the overuse of antibiotics in livestock supply chains. Within the Waitrose supply chain, all antibiotics are used carefully, under strict protocols and only in controlled circumstances; entirely healthy animals are not routinely given antibiotics, they are only used for treating ill animals or for those with pre-existing conditions.

“We maintain some antibiotics are important medicines to hold in the animal health armoury but must be used sparingly and only as a last resort.”

The Alliance to Save Our Antibiotics advises some basic measures to reduce antibiotic use on farms. These include leaving piglets with their mothers for a few weeks longer after birth, which drastically reduces the need for antibiotics to halt the diarrhoea associated with early weaning.

Fast-growing chickens, usually sent to slaughter only a month or five weeks from birth, can be replaced with slower-growing kinds less likely to fall prey to illness. Lower-stocking densities among indoor chickens also reduce antibiotic use substantially.

Among dairy cows, those raised indoors tend to suffer more from conditions such as mastitis, which requires antibiotic use. The Guardian recently found a large increase in the number of megafarms in the UK, where hundreds or thousands of animals are kept in large sheds, which has concerned antibiotics and animal welfare campaigners.

Cóilín Nunan, scientific adviser to the Alliance, said: “Much greater cuts in use are urgently needed if we are to preserve our remaining antibiotics. Intensive livestock farmers have much to learn from the practices of more extensive farming systems, which often have minimal antibiotic use.

“Moving to later weaning of piglets, using slower-growing chickens, lowering stocking densities of animals kept indoors and keeping cattle on pasture are all essential and achievable measures which can lower antibiotic use.”