Well the salvage place told me it's the length of the shaft that is important. All the VW's they had seemed to have the same gearbox end cv joint, but couldn't see inside the hub end to make sure that was the same.
Best bet is to get the yellow pages and take a trip to a salvage yard or 2 with the driveshaft you want to replace. The full driveshaft was £25. They could courier, but you really want to go and compare yours and be able to take it back if it's not right..