A major supplier of chicken to UK supermarkets is sourcing birds dosed with antibiotics “critical to human health”, according to a new investigation, as concerns grow about the spread of deadly superbugs.

The Bureau of Investigative Journalism (BIJ) and ITV found that the Polish meat business SuperDrob, which sells frozen poultry products to Lidl, Asda and Iceland, is sourcing chicken from farms that use fluoroquinolone antibiotics, classified as “critically important for human health” by the World Health Organization (WHO). Fluoroquinolones are often used to treat serious salmonella infections in humans.

Giving antibiotics to animals has come under increasing scrutiny, as scientists highlight the risks of potentially lethal bacteria developing antibiotic resistance, meaning drugs may no longer work to treat human infections. Antibiotic-resistant bacteria – known as “superbugs” – are a growing threat to human health, leading to an estimated 1.2 million deaths globally in 2019.

There are growing concerns that farmers giving these critically important antibiotics to their animals may contribute to the problem. To reduce the risk of superbug outbreaks, the EU tightened up laws about the use of antibiotics on farms last year.

Yet it appears that the use of drugs critical for human health on farms in Poland, Europe’s biggest producer of poultry meat, has soared in recent years. Sales of fluoroquinolones have increased by more than 70% in the country. Data shows even larger increases in the sales of colistin, a last-resort drug used to treat serious infections that have not responded to other medicines. The WHO classifies both as critically important for human health.

SuperDrob is one of Poland’s leading poultry producers and more than 50% of its revenue is from exports. Three sources, including a farmer who supplies chicken to SuperDrob and a vet who serves supplying farms, confirmed that fluoroquinolone antibiotics were being used, according to interviews conducted by the BIJ. There is nothing unlawful about this but testing undertaken by the BIJ, overseen by an Oxford University academic, in May discovered bacteria resistant to fluoroquinolones in samples of waste collected from a number of Polish poultry farms that are understood to have supplied SuperDrob.

SuperDrob said the drugs were in use, but that it had firm policies in place to ensure they were only used when justified. It said: “Where there is a veterinary need for medical treatment, then it is used under the supervision of veterinarians.” The company also said it was reducing the use of fluoroquinolone antibiotics and would phase them out by 2025.

Tim Walsh, a professor of medical microbiology at Oxford University, said he believed there had been a failure at an EU level to monitor antibiotic use in Poland, and that the country’s soaring sales of high-priority antibiotics should have raised alarm bells.

But the European Commission said that measures taken in Poland since a UK salmonella outbreak in 2020, including improved biosecurity on farms and better hygiene in meat plants, had resulted in a reduction of salmonella contaminations.

Although fluoroquinolone antibiotics are legal to use on chicken farms in the UK and EU under veterinary supervision, their use is now tightly controlled by regulators and they are not allowed to be used preventively on healthy animals. SuperDrob said its policies did not permit the use of antibiotics for prophylactic purposes and such behaviour was also prohibited for SuperDrob’s suppliers.

The Polish chief veterinary inspectorate said the prophylactic – or preventive – use of antibiotics was not common practice in Poland.

In 2020, EU and UK authorities identified SuperDrob meat plants and farms as the main source of the UK salmonella outbreak that infected more than 400 people. The BIJ looked at genetic sequences from bacteria responsible for the outbreak and found that most were resistant to fluoroquinolones and in some instances, samples were also found to be resistant to multiple drugs, making infections even more difficult to treat.

SuperDrob said that at the time of the outbreak the industry was supervised by the state, but that it had introduced its own system for the control of salmonella which had been developed by poultry disease and quality department specialists. It said it had also varied the contracts with its breeders to ensure that these systems were in place at their facilities. No similar instances had been detected in its products since March 2021.

Asda said all its imported frozen poultry products went through rigorous safety and quality checks. Iceland Foods said it prohibited its suppliers from prophylactically using antibiotics that were critical for treating diseases in humans. Lidl also said its suppliers were prohibited from using antibiotics as a preventive measure.

Asda said customers should always thoroughly cook frozen chicken products to reduce the risk of getting ill.