Asda had tonnes of the stuff out the fron of the store in Luton. Not sure if this is nationwide but picked up a couple of bags.
barcode is 5051413692967. showing on my receipt as 505141369296K.
serves it's purpose, i have grown a fair bit of stuff in this in pots over the year bought some to fill a hole and sprinkle some herb seeds on to try and attract beneficial bugs to the garden.
If someone can confirm if this is available at other branches would be pretty good.