An urgent investigation is under way to find out how Scottish salmon products on sale at Waitrose became contaminated with listeria.

The retailer today announced a nationwide recall of two own-brand items - smoked salmon parcels and a terrine - after routine testing discovered the bacteria.

In a statement the firm said consumers should not eat Waitrose Smoked Salmon Parcels 115g and Waitrose Scottish Poached Salmon Terrines 100g with best before dates up to August 28, 2007. Full refunds will be given for returned items.

Inquiries are focussing on the suppliers, Macrae of Scotland, part of the Young’s sea food groups, which has a plant in Livingston, near Edinburgh, dedicated to Waitrose products.

Production ceased on the premises on Sunday after listeria was detected and technical staff are now checking every stage of the process to establish the cause.

The disease is particularly dangerous for pregnant women and can trigger miscarriage, still or premature birth and illness in a new born baby.

Other groups at risk are the elderly, the very young and people receiving medical treatment that compromises the immune system, such as cancer patients having chemotherapy. For most healthy adults the risk is low but severe cases can lead to fatal complications, including septicaemia and meningitis.

Most people become infected from eating certain foods. Smoked fish, pâtés, soft cheeses, unwashed salad and cold cuts of meat are common sources of listeria infection for humans. These foods are frequently chilled for some time before consumption and listeria is unusual because its bacteria can grow at low refrigeration temperatures of below 5C.

Listeria however is also widespread in the environment and can be found in raw food, soil, vegetation, sewage and in the faeces of many mammals, birds and fish.

As a precaution Waitrose have also removed from sale a range of other seafood products including prawns and crab which are also purchased from the same supplier.

Consumers may have to do without some of these favourite treats for the next few days because the chain has also halted production of these items while investigations continue into the source of listeria.

A spokeswoman for Macrae’s said that the precise source of contamination had not yet been identified and it could have been soft cheese used in the products, the smoked fish itself or some other factor.

Every step of the production process had been examined however and the listeria was no longer present in the plant, she said.

A team of inspectors from Waitrose is to visit the premises, however, before production resumes.

Experts at the Health Protection Agency and Food Standards Agency are already concerned about the rise in listeria cases this year, which have so far resulted in 25 deaths including that of a baby.

Other items removed from sale by Waitrose pending inquiries are: Waitrose Prawn cocktail 200g; Waitrose Prawn cocktail reduced fat 200g; Waitrose Panamanian king prawns 200g; Waitrose Hebridean mini dressed crab 140g; Waitrose Mini dressed crab shells 420g; Waitrose Hebridean white crab meat 100g; Waitrose Dressed layered crab 200g; Waitrose Scottish smoked salmon tsar slices 110g; Waitrose Mini smoked salmon rings 190g; Waitrose Scottish smoked salmon ring 250g.

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