15. Return after due date and amendment of return.

If any person has not furnished a return within the time allowed under sub- section (1) of section 14 or under a notice issued under clause (i) of sub-section (4) of section 16, or having furnished a return discovers any omission or wrong statement therein, he may furnish a return or a revised return, as the case may be, at any time before the expiry of one year from the end of the relevant assessment year or before the completion of the assessment, whichever is earlier :

Provided that—