Have you tried the "frixion" ballpoint pens from Pilot - can get on Amazon - you can erase the line; you get rid of the line with heat from an iron. The line will reappear if you put you fabric in the freezer - so I guess what people are saying is that the line can reappear if it is really really cold. I love these pens because they glide onto the fabric without any snagging and punching up of the fabric. They come any many different colors - I think there are 8 pens in package for about $18 US. I am sure they have them in the UK somewhere.