There is a legal requirement to provide the details requested for the compilation of the electoral register. Failure to do so is a criminal offence and can result in a fine of up to �1,000.
Whether you wish to vote or not is not relevant. The electoral register has nothing to do with Council Tax.
However, these responsibilities fall upon the individuals and nobody else. Disregarding the Data Protection Act for a moment, third parties are not obliged to divulge information about (say) their clients except when ordered by a Court. Such an order is unlikely to be made in these circumstances.
The Data Protection Act (DPA) is designed to safeguard information held on living individuals. It is not designed (as many companies would have you believe) to prevent a Third Party making enquiries on behalf of somebody else. Nor does it dictate that companies �must only speak to Mr Smith and nobody else�. Companies may have these procedures in place for their own and their clients� protection and security, but it is nothing to do with the DPA.
You do not need to cite the DPA to refuse the request that has been made. The information you hold on your tenants is confidential to your business and need not be divulged. If the electoral registration department of the local authority concerned suspects someone of having failed to provide them with the information required by law, you are not obliged to assist them with their enquiries unless a court orders you to do so..