Thanks for the link and the second recommendation
@sleepingwolf and
@Lilian ! It's reasonably priced and has next day delivery so I will order some to give it a go, but I don't think it's what I'm after.
It says carbon paper rather than wax paper. The wax paper I like to use leaves a very solid permanent line, whereas carbon paper I have used previously (can't remember if it was burda or another brand) left a very chalk-y faint line that tended to disappear under the sewing machine needle or the iron. Obviously great if you want to have a line that disappears on your finished garment, and probably what most people want, but I am looking for something to permanently mark my underlining with no risk of vanishing.