Before you rush off to your lawyer - the term "loose leaf" is used to indicate it is not being sold in tea-bags.
Certain black teas, chiefly Indian in origin, are not sold in large leaf form, and cheaper teas generally are reduced to make them go further. We do not have a term "granulated tea", but really cheap teas are known as "floor-sweepings".
Take it back to Tesco's and tell them you are not happy with it and want it replaced. And in future look for good brand names or shop in a better store
