In which case you put in some tenancy agreement (or whatever) - that you have with Florrie - that she - by signing this agreement - agrees that her details can be passed on to sub contractors who need to look at her pipes (or whatever). Then you agree with the subcontractors that they must not...
I suspect hitony's company is the victim of some over cautious legal advice. I accept this does not help his situation but I doubt what the lawyers are suggesting is necessary.
It's all about taking 'reasonable' steps as far as I can see and if you need to forward Florrie Blennerhasset's...