Changed the battery and found it very difficult to get a 13mm socket on the clamp as the strapping got in the way.I don't know if the fitting bolt is standard also I noticed that the battery case holes have been elongated by the previous owner or garage. What is the standard method of fitting
Sounds standard, but never had any trouble myself. The webbing shouldn't be in the way of the bolt, though.
If it's a 13mm head, then its probably the earlier long bolt which should be dead easy. My later car has a short bolt but I think the head is 10mm.