Sorry missed the question about salt petre, no there is no need for saltpetre as mentioned previoiously there are advantages by using it as some say it can reduce the chances of botulism. However this is an old recipe used during the war when saltpetre was in short supply. I was always taught that the air curing is essential not just anothe phase of the process. I have done plenty of these and gammons in the same way and all really good, with the exception of a few salty ones.