i have been looking at sites, and generally most sites with fpp in my area come with a 5 yr occupancy clause, and regardless of having the clause, the purchaser would have to reapply for planning in their own name.
i suppose this is only a problem if the site has planning for more than one house, but even then the local authority will ask that an occupancy clause be applied by the first house only, however i'm not sure if this is always the case.
re: local need, i'm not sure but am assuming that once fpp has been given, it is a relatively small thing to change the name on the planning.
i've been looking up planning permission and have found a few sites for sale with a "local need" aspect to it, yet it is not featured in the details for sale, where the occupancy clause is, and considering market, people are more likely to buy sites for "their" house rather than to develop, small scale development, but i could be wrong?