(1 A) If the tax payable under sub section (1) remains unpaid for six months after the expiry of the time specified in the notice of assessment and demand or, the commencement of the Uttar Pradesh Bikri Kar (Dwitiya Sanshodhan) Adhiniyam, 1963, whichever is later, then, without prejudice to any other liability or penalty which the de faulter may, in consequence of such non payment, incur under this Act, simple interest at the rate of eighteen per cent for annum shall run on the amount then remain 135 ing due from the date of expiry of the time specified in the said notice, or from the commencement of the said Adhiniyam, as the case may be, and shall be added to the amount of tax and be deemed for all purposes to be part of the tax: Provided that where as a result of appeal, revision or reference, or of any other order of a competent court or authority, the amount of tax is varied, the interest shall be recalculated accordingly.