So I tried lighter fluid - did nothing. Then tried white spirit, left it on for 30 mins, again did nothing.
I resolved it by putting water, washing up liquid and some white spirit into a bottle, covering the bass with single sheets of toilet paper, dribbling the liquid over the bass, so the toilet paper soaks up the liquid, then tightly covered it with cling film. Left it for a day and a half. It was messy, but was able to scrap the residue off with the edge of a cd.
There were a few little marks leftover, but applied some lighter fluid, and it polished up nicely.