A consumer privacy group has called for a worldwide boycott of Tesco stores after the retail giant announced plans to expand trials of radio frequency identification (RFID) wireless tags.

US-based privacy organisation Consumers Against Supermarket Privacy Invasion and Numbering (Caspian) is concerned about the potential of item-level RFID tags to track consumers outside stores.

Caspian founder Katherine Albrecht said Tesco's expansion of trial stores from two to 10 could potentially involve hundreds of thousands more shoppers taking home items containing RFID "spychips". RFID technology is increasingly used in the retail industry but is mainly confined to distribution centres at present.

Tesco plans to install RFID equipment at loading and unloading bays, and at merchandise receipt points at its 1,300 stores and 35 distribution centres this year, forming a key element of its supply chain strategy.

But the supermarket giant has also begun tagging individual high-value items such as DVDs, causing concern among privacy organisations.

RFID tags may continue to work long after a product is bought and can be scanned through clothing, according to Caspian. As a result, individual items could be linked to a consumer's credit or store loyalty card, enabling retailers to covertly analyse purchaser behaviour.

"If consumers allow RFID tags to be broadly deployed on consumer items, abuses outside the retail environment will surely arise," predicted Albrecht. "Tesco's actions in promoting the item-level use of RFID is irresponsible in light of these potential dangers." This is not the first time that item-level wireless tagging has attracted controversy. Two years ago, more than 30 privacy and civil liberties groups signed a statement calling for the voluntary suspension of all RFID tagging of consumer goods.

However, security experts said a balance should be struck to allow consumers to reap the benefits of tagging.

"As long as RFID is properly advertised by the retailers, I'd be willing to forgo a little privacy for lower costs, increased availability and other benefits it could bring," said John Madelin, business development director at RSA Security.

Industry watchers predict that RFID will not be widely used for item-level tagging in shops until 2008. "Currently RFID technology is relatively crude and it's pretty unlikely that Tesco has the range to breach anyone's privacy outside the scope of a few metres," said Madelin. "We already have mechanisms to kill and jam the current tags and the ones available by [2008] will be advanced enough to integrate quite neatly into security systems."