Roy
The back button focus issue is just with the AF/ON button,for some reason it will not shift out of Zone AF,the star button next to it changes right through all the AF points no problem as does the main shutter button,this was never an issue when the body was new and only started to happen when I had the camera in to Canon Singapore for the second time,BTW this even happens when you take Zone AF out of the menu choice so a definite fault.
I bought the Body in Singapore last December but anything you buy there only has what they call a local warranty which lasts for a year to me or you but eighteen month for locals,tried exchanging body at the shop where I purchased it but they were having none of it and just kept saying You Go Service Centre which I did twice.
On return to UK I sent it in to Canon again with a letter explaining all the issues and that is when I received the phone call about the back button so anyone who knows their Canon camera can tell straight away that there was a rabbit away so to speak.
Anyway thanks for advice Roy and I will let you know if I get it sorted.
Cheers
Bob