Ayrprox & others - thank you very much for the time and effort you have put into your replies. Now I feel more able to give my colleagues an explanation as to how the airspace in which we operate is managed. The only bit that now puzzles me is why we ever needed to have an announcement in the first place of threshold elevation when is well documented. But it's not important so please don't spend effort answering.
Thanks & I might even make the call.
PM