The assessee shall not be entitled to produce additional evidence, whether oral or documentary, before the appellate authority or the Tribunal except where the evidence sought to be adduced is an evidence, which the assessing authority had wrongly refused to admit or which after exercise of due diligence was not within his knowledge or could not be produced by him before the assessing authority, and in every such case, upon the additional evidence being taken on record, reasonable opportunity for challenge or rebuttal shall be given to the assessing authority.