The proprietor of any lease under this Act may, subject to any provisions in his or her lease affecting his or her right to do so, sublet for a term not less than three years by signing a sublease in the form in Schedule 11 to this Act; but no sublease of any land subject to a mortgage upon the lease of the land comprised in the sublease shall be valid or binding against the mortgagee of the lease unless he or she has consented in writing to the sublease previously to the sublease being registered.