(5) Every company shall, in each financial year, on or before the date on which the first instalment, or where it has not previously been assessed by way of regular assessment under this Act, on or before the date on which the last instalment, of advance surtax is due in its case under sub- section (4), if it is likely to have any current chargeable amount, send to the Income- tax Officer,--
(a) where it has been previously assessed by way of regular assessment under this Act, a statement of advance surtax payable by it computed in the manner laid down in sub- section (3), or
(b) where it has not previously been assessed by way of regular assessment under this Act, an estimate of--
(i) the current chargeable amount and
(ii) the advance surtax payable by it on the amount specified in (i) above calculated in the, manner laid down in sub- section (3), and shall pay such amount of advance surtax,-
(I) in a case falling under clause (a), as accords with the statement in equal instalments on the dates applicable in its case under sub- section (4); and
(II) in a case falling under clause (b), as accords with the estimate in equal instalments on such of the dates applicable in its case as have not expired, or in one sum if only the last of such dates has not expired.