Well I gave it quite a thorough testing!
I had an old loco I had used for testing paint mixes and it was a bit of a mess.
First of all I used some oh a more expensive brand of oven cleaner, which used a sort of.....goo to clean, rather than the foam of Mr Muscle. I left the loco in that for 6 hours and it did a pretty good job, all the thin single coat stuff came off under a tap.
However the thicker stuff still hadn't budged. So I went and bought some Mr Muscle today, put the loco in my little tin, filled it with the stuff and left it for another 6 hours. washed it off and et voila! all the hand painted and airbrushed stuff was gone! one entirely clean, originally painted loco!
I took pics and as soon as I find the lead I will put them up!
Thanks once more for the tip.
Alex