I bought some Autoglym tar remover this morning. It’s very effective at removing tar spots, worked in an instant on the few I had. However it hasn’t made much of an impression on the sticker remains after quite a long slog. Quite a lot of black residue has come off on the cloth, and I’ve managed to chip off a tiny amount around the edge, but I don’t think this is going to remove anything like all of it. Can’t get my hands on a hairdryer at the moment, I’ll try that later, in combination with the tar remover. Part of the trouble is that the stuff that’s left is very thick, almost 1 mm I’d say, and attached so fast onto the paintwork that there’s no way for solvent to attack the surface in contact with the paintwork. This is really annoying!