We do the same. Doesn't everyone these days?
I hadn't thought about the legal implications, but had assumed that providing we only used the information for our own purposes and didn't pass it on, we were OK. But, thinking about it, I'm probably wrong.
We're trying to send out newsletters via e-mail and have asked specific permission to use members' e-mail addresses for this. But how do we stand if, say, the police wanted information? I've already had them phone me about one of our members who went missing briefly. (They thought he might be at the plot and wanted me to unlock.)
Our livestock owners are on a national database and last year DEFRA wrote asking their permission to pass on their details to government agencies in case of civil emergency. So perhaps we ought to use a disclaimer.
Any lawyers out there?