Thanks for your help Paul, I have not managed to find out if the actual glass manufacturer is a GGF member and because I'm mainly dealing with my supplier/installer I don't know if it's really my remit to sort of bypass them. I contacted Certass who the supplier are registered with but they have not bothered to reply!
I was hoping that someone here might be able to say if these sort of marks are generally thought of as acceptable or normal - I've been given a few days to let the company know if I'm still not happy with any of the other units but it seems that it's going to be a bit of a dispute about this looking in the sunshine business