Chickens for sale in Britain’s supermarkets are showing record levels of superbugs resistant to some of the strongest antibiotics, new research from the government has found.

The results are concerning because resistance to antibiotics among livestock can easily affect resistance among humans, rendering vital medicines ineffective against serious diseases.

The Food Standards Agency, which tested a large sample of fresh whole chickens from retailers, reported “significantly higher proportions” in the last 10 years in instances of campylobacter, a harmful pathogen, that were found to be resistant to the antibiotics commonly used to treat it.

The agency warned: “This survey provides evidence that AMR [anti-microbial resistant] campylobacter are to be found on whole fresh chickens sold at retail in the UK. It is therefore important to handle chicken hygienically and cook thoroughly to reduce the risk to public health.”

In 2014, the Guardian revealed high levels of campylobacter infection in UK chicken meat, amid hygiene and safety breaches in processing plants. The Guardian has also revealed the presence of the superbug MRSA – another superbug spread through infected meat – in UK pork products.

The FSA has also noted that the proportion of campylobacter-infected chickens which showed resistance to key antibiotics, in this case ciprofloxacin, “has increased significantly” compared with a previous survey of chickens sold at retail 10 years ago. More than 4,000 samples were tested, then samples of smaller numbers exhibiting campylobacter infections retested to detect whether they carried bacteria resistant to the key antibiotics. Ciprofloxacin resistance was identified in more than half of the samples of one form of campylobacter tested, 237 out of 437 tests on Campylobacter jejuni, and in nearly half (52 out of 108) of another strain, Campylobacter coli.

The results were taken by experts to show that the use of antibiotics to treat farm animals is giving rise to the spread of resistant bacteria, which can have major effects on human health because one of the main methods of transmission to many strains of resistant bacteria is through contact with livestock in the food chain. While proper hygiene practices and thorough cooking can kill the bugs, any lapses can result in serious infection.

Cóilín Nunan, scientific adviser to the Alliance to Save Our Antibiotics, told the Guardian: “It is scandalous that [government rules] still allow for poultry to be mass-medicated with fluoroquinolone antibiotics. Twenty years ago, a House of Lords report said this should be stopped. Even the US banned the practice over 10 years ago because of the strength of the scientific evidence. So why are British and European authorities still refusing to take action?”

Campylobacter can cause serious food poisoning and in severe cases death. Strains that are resistant to the antibiotics used against them are even more harmful, because their spread means more people – and potentially livestock – must be treated with antibiotics of last resort.

Doctors fear that using these final remaining weapons in the armoury of medicine will render them ineffective too, leaving us defenceless against germs that had previously been defeated. As a result, the emphasis in human medicine in most developed countries has moved in the last decade to preventing the spread of such diseases.

However, more than half of antibiotics used worldwide are administered to livestock, often to whole flocks or herds regardless of the number infected, and in some countries they are given out routinely to promote growth. This has led many scientists to conclude that farm animals are a leading cause of antibiotic resistance, a finding that appeared to be confirmed by the FSA study.

Efforts to reduce the use of antibiotics on farms, which have been strongly urged by the World Health Organisation and others, have been slow to take effect, while the problem appears to be growing.

More than a year ago, for instance, in response to separate data on the spread of campylobacter among chickens, the European Centre for Disease Prevention and Control, and the European Food Safety Authority, advised: “Given the high levels of resistance to fluoroquinolones in broilers [chickens bred for meat], and the assessment that a large proportion of human campylobacteriosis infections comes from the handling, preparation and consumption of broiler meat, this is a compelling example of how antimicrobial resistance in food and animals may impact the availability of effective antimicrobial agents for treating severe human campylobacter infections.”

However, no action has been taken to ban or restrict the use of these powerful drugs on farms. Farmers are reluctant to accept restrictions, because the best alternative may be to cull infected animals.