(4)Nothing contained in this rule shall affect the power of the Deputy Commissioner (Appeals) or, as the case may be, the Commissioner (Appeals) to direct the production of any document, or the examination of any witness, to enable him to dispose of the appeal, or for any other substantial cause including the enhancement of the assessment or penalty (whether on his own motion or on the request of the Assessing Officer) under clause (a) of sub-section (1) of section 251 or the imposition of penalty under section 271.
