Its cornmeal hun, tesco's don't seem to sell it but Sainsburys do although its the solid stuff they sell that you can slice and grill or fry, I prefer the polenta that you can make like mash, it's very nice, esp with loads of butter in (but we won't go there!!!!)
Ooh will have to try that! I love polenta, just had it for tea The sainsbury's by me sells the packets of grain polenta as well as the blocks but it's by the lentils etc. rather than the instant mash. Worth a scout round or an ask x
Most supermarkets do it, including Tesco. It's not always called Polenta though. Sometimes it's called Cornmeal... and it comes in coarse and fine. Try with the world foods. Or ask at the Customer Services desk.