Chickens sold in Britain are still being contaminated with high levels of the potentially deadly food poisoning bug campylobacter due to poor practice within the poultry industry, public health officials have warned.

Supermarkets have also continued to allow chickens to be sold to consumers even though they have tested positive for high levels of the bacteria.

Officials at Public Health England claim that without sufficient legislation the industry will resist implementing measures that could help to reduce the contamination of chickens for fear it will drive up the cost of meat. Their warnings come as the Food Standards Agency is preparing to publish a survey assessing the campylobacter levels on chicken being sold at leading UK supermarkets. Preliminary results showed that the bacteria could be found on the meat 59% of fresh chicken products on sale.

Dr Frieda Jorgensen, a microbiologist at Public Health England, said the updated results due to be published later this month are likely to show even higher contamination levels.

It comes after a Guardian investigation last month revealed how strict hygiene standards to prevent the contamination of meat could be flouted. It led to the health secretary, Jeremy Hunt, ordering FSA audits of two leading poultry factories while supermarkets carried out emergency inspections. The FSA audits found the factories were good and generally satisfactory.

But Dr Jorgensen said that common practices within the poultry industry were allowing biosecurity breaches that could lead to campylobacter infections spreading.

She said: “There are some thoughts that the way the industry is operating and the density of the industry can make it more difficult to prevent contamination of the flocks on the farm. “There is no doubt that industry practice has an impact on how easily it is spread from farm to farm. Applying strict biosecurity really can help. Industry practices are sometimes inadvertently causing biosecurity breaches.”

Around 60,000 people a year end up in hospital or have to visit a doctor in the UK as a result of campylobacter infections.

Jorgensen said, however, the real number of infections in people was more likely to be closer to 500,000 as many people do not go to see their doctor when they are infected.

She warned that an industry practice known as thinning – where farmers slaughter part of a flock to meet a retailers demand for smaller chickens before later slaughtering the rest – was a particular problem for causing infections.

The poultry industry in other European countries have stopped using the practice and have adopted other measures that have significantly reduced levels of campylobacter infections.

Jorgensen said the industry should consider freezing chickens that are found to be carrying the bacteria as this can reduce the level of contamination by up to 90%. Using nets to keep flies off flocks could also reduce the risk of the bacteria being spread between flocks. However, she said that the industry in the UK had yet to take these steps because of the cost implications.

She said: “If you go into a shed to slaughter half of the chickens at a younger age to get a certain size and the rest later then that constitutes a considerable biosecurity breach. In Iceland they have stopped doing this. That together with freezing every batch of chickens that test positive for campylobacter has resulted in a substantial reduction in the number of human cases. All of those cost money to put in place in the big, busy processing plants, but they are looking at whether it does bring a sufficient amount of reductions and if it is worth putting in place. At the moment there is no legislation in the UK like specifically dealing with campylobacter contamination.”

The British Poultry Council, which is the trade body for the poultry industry, said the industry carried out tests for campylobacter on around 5,000 chicken flocks a year when they go for slaughter. The results are then shared within the industry and with retailers, including supermarkets.

However, Richard Griffiths, the director of food policy at the council, admitted that even if birds test positive, the chickens are still sold by supermarkets.

Unlike salmonella, another common food poisoning bacteria found in chicken, there is no legislation to prevent meat contaminated with campylobacter from being sold to the public.

According to British Poultry Council figures tens of thousands of birds from 2,928 infected flocks have been allowed to go on sale in the past 12 months to September 2014. Griffiths said that although consumers were not told of the risk, the tests were fed back to poultry producers to help them improve their biosecurity.

He said: “The poultry producers use these results to inform the success of interventions they have implemented in the production chain, and to improve them where possible.”

The Food Standard Agency is now trialling two new techniques for reducing campylobacter levels on meat in two major abattoirs. One involves blasting carcasses with liquid nitrogen to kill the bacteria and the other uses ultrasound and steam to knock the bacteria off the meat.

A spokesman for the FSA said: “The quickest way to tackle campylobacter is for the food industry to take voluntary action. We are looking to retailers and their suppliers to introduce a range of actions now to help reduce the risks to the public from campylobacter, which is currently the biggest cause of food poisoning in the UK.”