(1) Tax in respect of any relevant residential property required to be included in a return under section 15 shall be due on 1 November immediately following the valuation date to which the return relates and tax so due shall be payable by the assessable person without the making of an assessment; but tax which has become due as aforesaid may be assessed on the assessable person (whether or not it has been paid when the assessment is made) if that tax, or any part of it, is no paid on or before the due date.

(2) In any case which -

(a) a return under section 15(1) is not delivered by an accountable person to the Commissioners on or before 1 November immediately following the relevant valuation date, or

(b) the Commissioners are dissatisfied with any return made under section 15(1),