(a)in the case of a company not being a company in which the public are substantially interested and other than a company referred to in clause (b), no loss incurred in any year prior to the previous year shall be carried forward and set off against the income of the previous year, unless on the last day of the previous year, the shares of the company carrying not less than fifty-one per cent. of the voting power were beneficially held by persons who beneficially held shares of the company carrying not less than fifty-one per cent. of the voting power on the last day of the year or years in which the loss was incurred;
