More than a million Cadbury chocolate bars are being taken off the shelves around Britain and Ireland over fears that they may have been contaminated with salmonella.

Cadbury-Schweppes said that it had agreed to recall seven of its most popular products in the UK as a precautionary measure after consultation with the Food Standards Agency (FSA).

The affected products are the 250g Dairy Milk Turkish, Dairy Milk Caramel and Dairy Milk Mint bars, the Dairy Milk 8 chunk, the 1kg Dairy Milk bar, the 105g Dairy Milk Buttons Easter Egg, and the 10p Freddo bar.

The contamination was detected at Cadbury’s Marlbrook plant, near Leominster in Herefordshire. A Cadbury spokeswoman said that it was due to a leaking pipe bringing cleaning water into the plant, which has now been fixed.

"We have the most stringent standards for testing for salmonella, more even than the Health Protection Agency levels," she said. "We found it in minute traces, which were well below the level that could raise any kind of alert, which is in itself below the level that could cause any kind of illness."

Salmonella is one of the most common causes of food poisoning and can be fatal. The bacterium is mostly found in poultry, eggs and unprocessed milk but can also be carried by water.

The Cadbury spokeswoman said that at a level of 1 million cells per 100g of product, it was generally considered that salmonella could cause mild stomach upset. The company's standard alert level is 10 cells per 100g, but the current contamination was measured at only 0.3 cells per 100g.

"One scientist called it a vanishingly small amount," the spokeswoman said. "But the consumer comes first."

She said that the total number of chocolate bars recalled would be "in the order of" a million, but the batch actually affected was much smaller than that. The company expects to have fresh stocks of the products back on the market in the near future.

The factory at Marlbrook generates 97,000 tonnes of milk chocolate crumb every year. It processes 180 million litres of fresh milk, 56,000 tonnes of sugar and 13,000 tonnes of cocoa liquor annually in the production process.

The crumb is transported to other sites at Bournville, near Birmingham, and Somerdale, near Bristol, to be blended with cocoa butter and turned into milk chocolate.

Cadbury said that anyone who had eaten a chocolate bar over the past few days should not be concerned. A spokesman said: "The levels are significantly below the standard that would be any health problem, but we are taking this measure as a precaution.

"If there are people who have eaten one of these chocolate bars today they should not worry, but they can get in touch with us if they are concerned for a full refund."

The free helpline number for Cadbury is 0800 818181. Uneaten products should be returned to Cadbury Recall, Freepost MID20061, Birmingham B3O 2QZ, and a refund will be given.

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