(a)Where refund of any amount becomes due to the assessee under this Act, he shall, subject to the provisions of this sub-section, be entitled to receive, in addition to the said amount, simple interest thereon calculated at the rate of one per cent, for every month or part of a month comprised in the period or periods from the date or, as the case may be, dates of payment of the tax or penalty to the date on which the refund is granted.