Anyway, I have a solution... I followed a discussion elsewhere that noted that it was quite easy to get them to transfer to the glue on a post it note, which I found to be true, but how to make the surface of the model similarly sticky without ruiningg the painted finish?
Opening one of my cupboards I noticed a jar of Staedtler Fimo Size for leaf metal which is sold for sticking leaf metal to Fimo polymer clay. Instructions are to paint a thin even layer then allow to dry for 15 minutes. I did this straight on to the model which had been painted with aqueous acrylics, and it gave a slightly sheened surface, *very* slightly tacky, but less so than a post it note. Then applied the decal using masking tape to hold it in place as usual, and rubbed it down... and it worked. I then applied another six transfers in the same way, so not a fluke.

















