I’ve done a couple of these Richie, and as Robert says, white spirits will do the trick. Its hard work, but I found if I left it soaking for a few minutes, then rubbed with a mesh-type cloth, the worst will come off fairly quickly.
Hardest bit is when you think its all cleaned off (you may have to use a window scraper carefully for some bits). It always seems to leave a faint shadow of residue that just won’t move. I’ve found a mini scrubbing brush (the type you’d use to clean finger nails) will break up this left over residue, then another dab of white spirits and a good scrubbing with a cloth, done.
Longest job so far was just over 4.5metres by .7 of a metre, virtually all covered in vinyl. The new vinyl wasn’t giving a total coverage, so the backing had to be clean. All in all, the whole cleaning process took about 2 hours, but boyo boy did my arms ache after that one. There’ll be a way of doing it by machine (a bonnet buffer maybe) but I haven’t had a go at this yet, anyone else tried a machine of some description?
Cheers, Dewi