So i followed your advice, I preheated the hot-end to 120deg, then tried to gently remove the PLA. It was stuck pretty hard so I took the fan shroud off, and managed to remove a bit from around the nozzle - the pla had gone kinda putty like from the heat.
The rest of the "fossil" though is quite brittle, and I am worried I am having to use too much force to remove it, I was thinking that I could up the temp to around 210 ish and leave it for a while and hope that the lump kinda melts itself off a bit? Is that a bad idea? I also have a heat gun (a turbo 1200wat hair dryer kinda thing for heatshrink etc in the workshop), I might also be able to use that to apply heat to the further away bits?