I rang my local dealer today who had no idea whether the 14" Panda steels would fit a 100HP, nor indeed whether the 15" steels from a GP would.
Luckily about an hour later a wrecked GP was unloaded from a recovery truck at my body shop and it's a definite write off, so this weekend I'll be seeing whether the 15" steels do in fact fit.
If they do, the tyre size will need to be changed from 165/65 to 175/50 to retain the same rolling radius as the 100HPs 195/45s, but winter tyres are available in that size anyway so it's no problem.
Will report back when I'm done!
GP wheels are 4x100 - you'll be needing 4x98 won't you?