Per provider Jan 2016 - This API has now been turned off. Stay tuned for the new version.
The Tesco API gives you access to the vast grocery catalog of the third largest retailer in the world. Tesco's Grocery API has the ability to allow you to search for products using text or barcode, by dept/aisle/shelf categories, all special offers, and even previously bought 'favourites'. You can add/amend/delete items in the basket.