A Briton accused of trying to blackmail an American supermarket chain by threatening to poison jars of baby food pleaded not guilty at a court hearing today.

David Dickinson, 43, of Middlesbrough, has been indicted on two charges by a grand jury in California and a trial date set for July 13.

He entered his plea during a court appearance in Los Angeles, according to Thom Mrozek, spokesman for the US attorney's office in Los Angeles.

If convicted Dickinson faces up to 25 years in jail.

Dickinson is being held in custody after a court in Los Angeles deemed him to be a threat to the community and a flight risk.

He was arrested earlier this month and charged with one count of extortion and one count of tampering with consumer products.

Dickinson, who was living with his family in the Venice area of Los Angeles on an expired visa, allegedly sent a bizarre threat to a corporate office of the Ralphs supermarket chain.

The package included four baby food and formula products, and a note labelled ''blackmail demand'', prosecutors said.

Days later a separate letter was sent demanding that £100,000 be put into a bank account. If the company did not comply, jars of tainted baby food would be placed on the shelves of its shops, the letter said.

The letter ordered that the company distribute 9,000 cash machine cards at stores in Santa Monica, San Diego and San Ramon that could be used to access the account.

The letter further demanded that Ralphs place an advertisement for a ''German tuba'' in the March 25 issue of a Los Angeles classified newspaper and instructed that the PIN number to access the money be listed as the tuba's model number.

Tests on the food products sent in the package revealed that a container of Gerber orange juice contained more than 50% hydraulic fluid. Boric acid was found in a jar of horseradish and a container of Similac infant formula. A jar of Gerber carrots also was found to contain glass shards.