Got it sorted!
The super helpful guys at MJA Land Rover in Bromsgrove managed to get it off (took two of them and much bigger tools than I have)
Apparently, at some point someone decided it was a good idea to put loads of thread lock on the bolt so that explains the difficulty.
Just need to wait for the engine to cool down now so I can get on with doing the timing belt.
Thanks to everyone who provided advice - much appreciated.
Edit: forgot to say, the old hub got so mangled getting it off that I'm putting a new viscous fan on (once I've cleaned all the threadlock off the bolt)