Assessment of unregistered taxable persons: authorities may assess liability by best judgement, subject to a hearing opportunity. The proper officer may assess a person who failed to obtain or whose registration was cancelled but who remained liable to tax, to the best of his judgement for the relevant tax periods and issue an assessment order within a time limit measured from the annual return due date for the financial year to which the unpaid tax relates; provided that the person is given an opportunity of being heard.