ginge, read carefully.

get some rope, start at the bottom of the pully, rap cloackwise round the pully 1 and 1/2 turns so that it goes all the way round and back over the begining of the rope. then it comes off the top of the pully to the right.

find a bracket or something solid on that side of the engine.

now when u turn the bolt anticlockwise the rope should tighten up on itself. this will stop the pully from moving and therefore the crank.
now u should be able to put ur socket on it and apply as much pressure as needed till it goes.
now i did this and snapped the rope twice, then i got another bit or rope and the blow tourch, and that time it went.

shocking it like that will help more then as well as the rope will increase the amount of force from the hammer get transfered to the bolt.
if u know what i mean.