TWO North-East supermarkets sparked a nationwide salmonella alert after fresh basil tested positive for the bacteria.

The Food Standards Agency (FSA) issued a warning to people who had bought the herb from Asda, Sainsbury's and Somerfields not to use it in case they came down with diarrhoea and sickness.

Salmonella was discovered on samples on sale at the Asda stores in Peterlee and Bishop Auckland, both County Durham, a Sainsbury's store in Gateshead, as well as a Somerfield store in Hertfordshire.

An FSA spokesman said: " Some of the 'display until' and 'best before' dates on the affected packets will have expired and the product will have reached the end of its shelf life. The affected basil is also labelled as 'wash before use'.

"However, it is possible that people may still have some affected batches at home. For example, they may have used the basil to make fresh pesto sauce or used it as an ingredient in other uncooked foods. Also some people may have frozen the herb.''

"Sainsbury's and Somerfield have informed the Agency that they have withdrawn all their potentially affected basil stocks with a best before date up to and including May 28.

"ASDA has told the agency that the only affected batches sold through its stores are those with a display until date up to and including May 18.

"Agency advice is that people who have bought basil from Sainsbury's and Somerfield with a best before date up to and including May 28 should take it back to the store where they bought it.

"People who bought basil from ASDA with a display until date up to and including May 18 should also return it to the store they bought it from.''

The chains have confirmed that none of the affected batches are still on sale. The FSA is investigating the possible source of this problem.

A spokesman for Asda said: "There were a couple of batches from Israel, quite small batches, with a date code to display until May 15 or May 18.

"Basil only has a short shelf-life so it is highly likely that people have used it already.

"There is a slight chance that people may have frozen. If they have they should bring it back and we will give them a full refund.''

The spokesman said that the store had had no complaints from customers and was not aware of anyone falling ill from using basil bought from its stores.

He added that the chain was still selling basil, but it was from a different batch and was not subject to the alert.