If the assessee fails to furnish the return within 15 days of issue of notice under section 46 then the Proper Officer may assess the tax liability in to the best of his judgment, taking into account all the relevant material available on record, and issue an assessment order. This is also known as ‘best judgment assessment’.
It can be completed without giving notice of hearing to the Non filer assessee.
Another important aspect is, in case an order of best judgment is passed under section 62 and returns are not filed within 30 days, the order becomes final and even if returns are filed subsequently, the order CANNOT be withdrawn.
Only remedy will be to file such returns and also prefer appeal under section 107.