63Deduction from rent etc. of rates by certain tenants of mines.
Any lessee, licensee, or grantee of a mine rateable by virtue of section 16W) of this Act whose lease, licence or grant was granted or made before 6th April 1875 may, unless before that date he had specifically contracted to pay any rates in respect of the mine in the event of the abolition of his exemption from being so rated, deduct from any rent, royalty, or dues payable by him during the continuance of his lease, licence or grant, or before the arrival of the period at which the amount of the rent, royalty or dues is liable to revision or readjustment, whichever is the less of the following, that is to say—
(a)one half of any rates paid by him in respect of the mine; or
(b)one half of what those rates would have been if calculated upon the rent, royalty or dues so payable by him.