Just to finish this story off.
The car was bought by a Land Rover mechanic. He's pretty sure the crank has snapped. Says these engines are notorious for it and he does about 3 a week!
Obviously my mate is gutted and he's lost a serious amount of cash on this episode of Land Rover ownership but what can you do when the Green Oval Goblin sneaks up and kicks you in the knackers? One thing is for certain, I wouldn't touch a Disco 4 diesel with yours. I'll stick with my old P38, thank you very much.
Thanks to everyone for their help and suggestions. I'm off back to the Rangie section. I'll get my butler to distribute some tea and biscuits later on ...