Well, a further development today, put the car up on the trolley jack today at the back end, one side at a time to have a gander at bushings, no obvious signs of wear or excessive movement. Installed my plenum spacer today and duly went out for a couple of test runs, could I reproduce the clunking, could I heck as like!!!? Could it be that I've inadvertently temporarily cured the problem when i jacked the car up this morning adn does this now point towards drop links?