So I get the electric heat gun out, however this won't get the frame hot enough. So next I get the propane torch out and heat the BB shell up to a decent temperature, still no luck.
So I took the seat post out, filled the frame with GT85 and walked away, fettle unsuccessful.
So after yesterdays unsuccessful fettle I brought out the big tools (literally).
I tipped the bike upside-down (I know, I know, but it wouldn't have worked in a work stand!) and clamped a small/portable vice on to the spanner flats of the adjustable cup. I then put two fairly large bolts through the bench-mounting points for the small vice. Next step, I used a g-clamp to fasten the vice on to the adjustable cup securely to ensure it wouldn't slip off.
Next I applied heat with the blow torch, and when hot enough, put a six foot professional mechanics extension bar (OK, an old bit of a kids climbing frame) between the two bolts and levered the heck out of it until the rust gave way (which took a lot of force on the end of the bar).
I had to reset the rig a couple of times to turn it a bit more before it was loose enough to be able to be turned with set of vice grips, but I finally got it out of the frame!
Here's the state the BB was in.
Fettle successful!
I'll get a new cartridge BB on order soon. Tomorrows job, the hubs.
Disclaimer: This isn't one of my bikes - Mine would never get in such a state!