Provided that nothing in this section shall be construed to entitle any person to deduct from the rent payable by him more than the whole sum deducted from the rent payable to him.

Redemption of charge for improvement expenses At any time before the expiration of the period for the payment of any improvement expenses together with interest thereon the owner or occupier of the premises on which they are charged may redeem such charge by paying to the Commissioner such part of the said expenses and such interest due, if any, as may not have been already paid or recovered.