Penal interest relief: waiver authorised for specific hardship cases involving late returns, advance tax defaults, and search-related loss. Authorisation permits reduction or waiver of penal interest under sections 234A, 234B and 234C where hardship arises: books seized in searches preventing timely return preparation; cash seized that could not be applied to tax instalments; unanticipated income (excluding capital gains) taxed after instalment dates with tax paid thereafter; retrospective law or judicial changes making earlier exempt receipts taxable; and voluntary, undetected filings delayed for reasons beyond taxpayer control. Relief applies from assessment year 1989-90 onward subject to conditions.