I believe the government had good reason to send out these lists.
Nonetheless, the committee should consider this: the current provisions in the legislation, which only address a person knowingly using information contained in this list, were developed with consideration to the fact that the only information on the list would be name and address. Now we are talking about a personal characteristic.
Your example was about a person working at an MP's office who leaves the list lying around where someone could access it and use it in a manner that does not comply with the law. As far as the offence is concerned for knowingly using information from a list of electors, there would be no way to prosecute someone who works at an MP's office, at a candidate's office or at the office of a registered party.