@ Dutch Master - No I didn't try "proper" turps. It can be obtained but not that easily, since it was replace with "White Spirit" as a paint cleaner/thinner.
So far, I've tried white spirit, surgical spirit (isopropyl alcohol), the Toluene/n-hexane based glue remover, "Brake cleaner" (which would normally have Trichlorethane in it - except the only one I could get the other day didn't). The only stuff that I've had limited success with, is Xylene based "Carb Cleaner" (Silkolene product - previously used for my motorcycle).
I've had a few other suggestions to try like a "Tar and Glue Remover" that contains Trimethylbenzene in it - used in the motor industry for car valeting - not sure where I'd find that though. Plus cigarette lighter petrol (as opposed to gas) - which is napthylene based. I'd actually forgotten all about trying that as it's been known to clean all sorts of things.
@ pootman - No, I hadn't thought of trying steam. Last time I tried any heat was when they'd come fresh out of the dishwasher - so they'd have been about 50 degrees C - I suspect that it'd be as you say and that steam would get them hotter though.
As for help/information on the label (or phone no's etc)? Well, unfortunately, I discovered that Gales are no longer a "proper" company that might offer help etc, they're just another brand of the "food nazis" a.k.a. Nestle.
Trying to get anything out of them, unless it's something official caused by VVV bad PR, is like getting blood out of a stone - in any case, it's probably just bought in in bulk and bottled by some faceless sub-contractor - I understand this kind of stuff, as I often carry some products of that nature in my truck (food products, but just not the kind you'd normally find on the shelves of your local supermarket). So I suspect that'd be a dead end.
I'll keep at it though, the lighter petrol, steam and if need be, I'll go to the local car paint supplier and get some cellulose thinners - I've never heard of anything that can resist that! But there's alway a first time I suppose!
"What the large print giveth, the small print taketh away". Tom Waits