Food Standards Agency tests have revealed almost three quarters of shop-bought fresh chickens were contaminated with food poisoning superbug campylobacter.
The food safety watchdog found 73% of the 4,011 chickens it studied tested positive for the presence of the bug.
Of Britain's biggest retailers, Asda had the highest percentage of positive test results with 80.4% while Tesco had 66.5%.
Campylobacter is a food bug mainly found on raw poultry and is the biggest cause of food poisoning in the UK.
The survey, which was conducted between February 2014 and February 2015 also found 19% of chickens tested positive for campylobacter within the highest band of contamination.
Packaging fared better, with only 0.1% testing positive for the most dangerous strain of the bug.
Retailers M&S, Morrisons, the Co-op and Waitrose were singled out for making strides at cutting contamination.
Agency director of policy Steve Wearne said "I want to challenge those retailers who haven't yet demonstrated the impact that M&S, Morrisons, the Co-op and Waitrose are having on reducing campylobacter on chickens on their shelves.
"We expect all retailers and processors to be achieving the reductions we have seen in these retailers' figures – that's the only way we will meet the target we all signed up to."
The tests would be repeated again this year to monitor progress, Wearne added.