Failure to deduct tax shielded where the payee files and pays tax, subject to accountant certificate and interest rules. A conditional exemption from being an assessee in default is introduced where a resident has filed a return, included the sum in income computation, paid the tax due, and the deductor furnishes a prescribed accountant's certificate; if not treated as an assessee in default, interest is payable from the date tax was deductible to the date the resident files the return. The limitation period for certain proceedings is extended from four to six years and an Explanation defining 'accountant' is inserted.