A regular pencil works just fine - it'll wash out in the end. And for marking dark fabric I use a Nonce pen (white). I am not sure if you can get that in the UK, but you can order it from Hancocks in Paducah (www.hancocks-paducah.com) I am in Germany and stock up when I am in the States. But I have used a regular white pencil when I ran out, and that worked okay too. Don't use the pens that you can make disappear with cold water (sounds just great, doesn't it!) but that blue color can come back, and then it's permanent. It's also permanent if you mark your quilt/pieces and the sun shines on it - the color changes to brown and is permanent. A hot iron has the same effect.