Well, I managed to stop the creaking, for now!

I yet again stripped out the rear and carefully looked just what could cause the creaking. Eventually it was found to be the top damper bush. After removing it, cleaning the area and the bush and lubing it up with silicone grease it seems to have cured it. However they have begun to perish so I reckon that Floflex replacements (as variable as their reputation is!) will be the only option...

On another note bar a mishap at a trackday it's been lovely to drive for a change.