Assessment of non-filers: best judgement order permitted; filing a valid return withdraws order but interest and late fees persist. If a registered person fails to file a return after a notice under section 46, the proper officer may assess tax to the best of his judgement and issue an assessment order within five years from the date specified for filing the annual return for the relevant financial year. A valid return filed within sixty days of that assessment order results in the order being deemed withdrawn, though interest and late fee liabilities continue; an additional sixty day extension may be availed on payment of an additional daily late fee, with the same effect upon filing.