Seven in 10 of chickens sold in the UK are infected with the potentially deadly campylobacter bug, it was revealed today.

Asda had the highest levels of contamination, with 78 per cent of tested birds infected - 28 per cent with the highest levels.

Co-op came second, followed by Morrison's, Sainsbury's and Waitrose.

Marks & Spencer had the second worst percentage of chickens testing positive for the highest levels.

Tesco had the lowest rates of infection, with 64 per cent of tested birds being positive, 11 per cent at the highest levels.

The supermarkets were named and shamed for the first time today under a move by the Food Standards Agency to improve public health.

An estimated 280,000 people in the UK suffer from campylobacter each year, with it proving fatal in 100 cases - making it the deadliest form of food poisoning.

Steve Wearne, the FSA's director of policy, said: "Levels of campylobacter have been far too high for a long time and they need to come down."

The FSA tests on 1,995 fresh shop-bought chickens between February and August found 70 per cent tested positive for campylobacter across the industry, with 18 per cent having the "highest levels of contamination". The bug was also found on six per cent of packaging. There is no safe minimum level of campylobacter.

Retailers have now committed to reducing the percentage of chickens carrying the bug to 10 per cent by the end of next year.

Mr Wearne said: "The incidence of campylobacter at the highest levels in Asda is significantly worse than the industry average, and the incidence of campylobacter at the highest levels in birds from Tesco is significantly lower than the industry average.

"Wherever you buy chicken from, they may have campylobacter. No individual retailer or the industry as a whole is yet meeting the target that they have agreed for the end of next year relating to the highest level of contamination in poultry."

The FSA advised people buying whole chickens not to wash them before cooking, and to ensure they were piping hot before being eaten. Cooking will kill campylobacter.

Lidl and Aldi were included in a group of smaller retailers where the average infection rates were 76 per cent - with 25 per cent having the highest levels. However the retailers were not named individually due up the small number of chickens tested.

Turkeys also carry campylobacter but at lower levels because the birds tend to be older at the time of slaughter.

Free-range chickens are thought more likely to carry campylobacter as it occurs naturally in the ground.

Since the FSA first revealed infection rates, Marks & Spencer and its supplier 2 Sisters Food Group have developed a plan to reduce campylobacter.

Asda has installed steam cleaning of birds at its supplier, Faccenda. A number of retailers have introduced "roast in the bag" chickens to prevent the bug being spread by consumers.

The previous results, announced in August, revealed that the bug was present in 65 per cent of birds tested. In four per cent of samples it was identified on the outside of the packaging. Retailers were not named at that stage.

The British Poultry Council said it viewed today’s data “as another step to reduce the number of cases of food poisoning by raising awareness amongst consumers”.

The BPC said: “Over the last five years the poultry sector, with retailers and the FSA, has worked hard to understand how this naturally occurring bug gets into flocks, how we can stop it and how we can remove it once it’s there.

“It is right that consumers have plenty of information on which to base their buying decisions, be that on safety, welfare, convenience or price.”