For anyone that's interested, a follow-up to my travails from last week relating to crank removal: I finally managed to get them off by the application of extreme leverage, achieved by lengthening the spanner something in the order of three feet, using a vacuum cleaner extension tube.
The next ordeal was getting the bottom bracket out. This I eventually accomplished by gripping the bottom bracket tool in a large alligator grip, which I then held in place in the workbench. I then applied the bottom bracket to the tool, frame and all, and turned the frame. Still hard work but deeply satisfying when it finally came off.
All I can say is that without the excellent advice picked up in urc I would still be struggling with the cranks, probably minus a few layers of skin off my knuckles. So, thanks all.
I once asked an engineer friend of mine the difference between power and torque. Another friend was in the room, and he replied "power is money, but torque is cheap". Made me laugh, anyway.