I think the interesting part of this is how to prevent the sending of data whether by email/fax or however which is the result of a simple number transcription error or fat-fingering. My first thought is white-listing but it's going to be a PITA to set up and get every one to use.

Where does the fine on the council go? It should be used by an gov run department to alter the councils processes or equipment to prevent the error reoccurring the measures being applied across all gov depts carrying such sensitive info; I'm going to guess it won't be.