Thanks for the input chaps !

Richard - sounds like yours has something to get hold of - mine is inset if anything , so 'grabbing' it is not an option unfortunately.

Tim - are you thinking soft or hard solder ? Woudlnt soft just snap off , and hard would mean getting it extremely hot and destroy the wiring in the tube - or am I missing something?

I am wondering if I can grind it out with a fine bit in a dremmel and hopefully the bits will clear. This baby is not going to budge by rotation. Then once I get the tube out the grub screw bears on clear the threads out with a tap , even going up a size in the threads if necessary.
Needles to say I am going to use a headed screw to replace it.