I saw this on Facebook today. Tesco has been remarkably quiet on the subject - perhaps they were waiting until the scheme was completely set up.
The deal is that you pay a deposit the first time you buy a product, and return the empty container for the next time you order (or to any participating store, not just Tesco) to be professionally cleaned and refilled. A lot of the products are in identical containers, which must make the cleaning process more efficient.
It looks very good on the surfa(and the Loop site is interesting) but the prices do seem quite high. The quantity in each container varies from one product to another - you'd have to work out the price per 100g for yourself for comparison.
It'll be for the Waitrose shopper level to start with, I am sure, but they have a 10%-off-your-first-order-offer. The choice of products is limited at the moment, but they are planning more.