I think until you've had an issue like this, it is difficult to imagine how the situation arises and what to do about it. In a past role, I had an individual who started by asking about the council's "attitude to health and safety". We treated it as a FOI and send copies of the H&S Policy document, monitoring reports etc. He kept on, writing several times a day about "attitude" to subjects and each time was pointed towards policy documents etc. many of which clearly showed "attitude" in terms of statements like "the council takes X seriously" or whatever and followed by the steps being taken to support that. He was never satisfied and for a period of about six weeks sent upwards of 300 emails, taking up staff time both in responding and copying multiple documents (he wanted them posted, not emailed). Suddenly he stopped and we heard he'd started on a local charity with the same demands. However much we wanted to respond it was never good enough.
Frankly, I don't think a policy would have helped either but we had reached the point when he did stop of considering ignoring the multiple emails and letters as they were just too time consuming and we were getting no where.