If Tesco made their data minable why would you go to Tesco's page again?
It's probably not in their best interests, so it's probably not something many sites will do. Most places are a bit cagey with their data. Unless it's publicly accessible, eg Spark's is the USDA database. No idea if Spark would even have the legal right to make it slurpable off Spark - maybe Tesco doesn't have the legal right to share their data out?
Deb, in New Zealand