The profits or income arising from rents of land and improvements thereon shall be the gross rent which is receivable and can be recovered after deducting therefrom rates borne by the owner and, where the owner undertakes to bear the cost of repairs, twenty-five per centum of the balance, but shall, where the rent recoverable in respect of such land and improvements is not restricted by any law for the time being in force, be not less than the net annual value after deducting therefrom any part thereof which is the income of the occupier within the meaning of paragraph (d) of section 3