Thought I'd give an update on my problem. The shop concerned was very difficult to deal with, wouldn't return messages etc so as I needed a working lens for my work I bought another copy which worked perfectly - such a nice lens. However it took up until today to get a refund, I sent metadata to them first which showed the fault then the lens once they asked for it. But surprise surprise when they got it they said there was nothing wrong with it and it was my cameras that were faulty. Basically it was weeks and weeks of hassles until today, at least I got a new lens (from another shop) that works a treat and I got my money back, except for postage as they still deny the lens is faulty.