Section 12. Recovery of tax from occupier of portion of land or building.

On the failure to recover any sum due on account of tax from the person primarily liable therefor, there may be recovered from the occupier of any part of the land or building in respect of which the tax is due, such portion thereof as bears to the total amount of the tax due the same ratio which the rent annually payable by such occupier bears to the aggregate amount of the annual letting value thereof.