And such a purchaser as ' is aforesaid shall be entitled to proceed in the manner prescribed by any law for the time being in force for the enhancement of the rent of any land coming within the fourth class of exceptions above made, if he can prove the same to 621 have been held at what was orginally an unfair rent, and if the same shall not have been held at a fixed rent, equal to the rent of good arable land, for a term exceeding twelve years; but not otherwise; Provided always that nothing in this section contained shall be construed to entitle any such purchaser as aforesaid to eject any raiyat having a right of occupancy at a fixed rent or at a rent assessable according to fixed rules under the laws in force, or to enhance the rent of any such raiyat otherwise than in the manner prescribed by such laws, or otherwise than the former proprietor, irrespectively of all engagements made since the time of settlement, may have been entitled to do.