an assessee engaged in the business of civil construction or supply of labour for civil construction, a sum equal to eight per cent of the gross receipts paid or payable to the assessee in the previous year on account of such business or, as the case may be, a sum higher than the aforesaid sum as declared by the assessee in his return of income, shall be deemed to be the profits and gains of such business chargeable to tax under the head “Profits and gains of business or profession”:
Provided that nothing contained in this sub-section shall apply in case the aforesaid gross receipts paid or payable exceed an amount of forty lakh rupees Any deduction allowable under the provisions of sections 30 to 38 shall, for the purposes of sub-section (1), be deemed to have been already given full effect to and no further deduction under those sections shall be allowed