Ok well it's off.
Ended up using a knife to cut the crappy glue, but unfortunately I cut half the wire and nipped the window washer fluid pipe too.
I'm supprised at how small the blob of glue is, feels far more substacial when poking around it and trying to pull the spoiler off!
It has litterally taken me from 11 this morning until 5, just to get the damn spoiler off.
And by the looks of it, the rubber gromit does't get seated right from factory, so i bet the mastic is a factory fix from a pre-production model, problem.
I have to fix the wire and hose, then I'll check the cause of the light not working and refit.
If i can i'll try to take some pictures and put a step by step guide to help anyone else having this issue, there's a lot of good information here, but put together in a guide with pictures should make the job 10x easier for anyone doing the same task.