(1) The Commissioner or any person appointed under sub-section (2) of section 9 to assist him, may at any time within two years from the date of any order passed by the Commissioner or by that person, as the case may be, on his own motion, rectify any mistake apparent from the record, and shall within a like period, rectify any such mistake which has been brought to his notice by any person affected by such order:
     Provided that no such rectification shall be made, if it has the effect of enhancing the tax or reducing the amount of refund, unless the Commissioner or the person appointed under sub-section (2) of section 9 to assist him, as the case may be, has given notice in writing to the person likely to be affected by the order of his intention to do so and has allowed such person a reasonable opportunity of being heard.
     (2) The provisions of sub-section (1) shall apply to the rectification of a mistake by an appellate authority under section 43 as they apply to the rectification of a mistake by the Commissioner.
     (3) Where any matter has been considered and decided in any proceeding by way of appeal or revision relating to an order referred to in sub-section (1) or sub-section (2), the authority passing such order may, notwithstanding anything contained in any law for the time being in force, amend the order under sub-section (1) or sub-section (2), as the case may be, in relation to any matter other than the matter which has been so considered and decided.
     (4) Where any such rectification has the effect of reducing the amount of the tax or penalty, the Commissioner shall, in the prescribed manner, refund any amount due to such person.
     (5) Where any such rectification has the effect of enhancing the amount of the tax or penalty or reducing the amount of the refund, the Commissioner shall recover the amount due from such person in the manner provided for in Chapter V.
     (6) Save as provided in the foregoing sub-sections, and subject to such rules as may be prescribed, any assessment made or order passed under this Act or the rules made thereunder by any person appointed under section 9 or by the Appellate Tribunal may be reviewed by such person or by the Appellate Tribunal, as the case may be, suo motu or upon an application made in that behalf.
     (7) Before any order is passed under sub-section (6) which is likely to affect any person adversely, such person shall be given a reasonable opportunity of being heard.