Note: this post was about adding Tesco product searching to my side-project APIfy. I've since took it offline as I don't have the time to maintain it.
Check out the Tesco Developers Portal and REST API Documentation for more information. Or drop the very helpful Nick Lansley, Head of Open Innovation @ Tesco Labs, an e-mail.
I'm also available for any work or consultation regarding Supermarket APIs, scraping, price comparison, etc - drop me an e-mail.