I tried Tesco but couldn't see it, but I am a bloke and just can't focus in this environment. However, I did find it in the baby/nappy section of Poundland. Two 100% cotton muslin cloths for £1, each measuring about 18 inches square. I'm told it's also available in Mothercare. If that fails, someone told me that a clean pillow case also works very well (for jam/jelly/cordial making etc).