(a)If upon any information which has come into his possession, the Commissioner is satisfied that any dealer, being liable to pay tax in respect of any period has failed to apply for registration, the Commissioner shall within one calendar year from the date of completion of the proceedings under sub-section (1) of Section 6 proceed, in such manner as may be prescribed, to assess such dealer and assess him to tax to the best of his judgement in respect of the whole of such period and shall impose upon him, by way of penalty, a sum two times of the amount of tax so assessed.