Holding occupied by more than one person

When any holding is occupied by or let to two or more persons, being severally responsible for the maintenance or payment of rent for the portions occupied, the municipality may for the purposes of assessing such holding, either treat the whole thereof as one holding, or, with the written consent of owner or owners of such holding, treat each of the said several portions therein or any two or more of several portions together, or each floor or flat as a separate holding.