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well, webbo/dave, i have to say your colleagues are 100% CORRECT!!! :o)
thank you so much for putting me out of my misery, there's no doubt at all that's what it is. i would never have guessed it was an annual, i checked all the perennials to no avail but really couldn't imagine that something so big and robus, and in flower in october, would be an annual. we drove past it again yesterday and could clearly see all the little black seed pod things hanging down from the black branches, bright green leaves and vibrant blue flowers, it really is a spectacular plant and i'm defo going to try and grow one next year.
many thanks again dave, i could kiss you :) :) :) xxxxxxxxxxxxxxxxxxxx