(1) An assessment shall not be made on a chargeable person for a chargeable period at any time before the specified return date for the chargeable period unless at that time the chargeable person has delivered a return for the chargeable period, and an assessment shall not be made at a time when the making of the assessment is precluded under section 955(2).
(2) Subject to subsection (3), an assessment made on a chargeable person for a chargeable period shall be made by the inspector by reference to the particulars contained in the chargeable person's return.
(3) Where -
(a) a chargeable person makes default in the delivery of a return for a chargeable period, or
(b) the inspector is not satisfied with the return which has been delivered, or has received any information as to its insufficiency,
nothing in this section shall prevent the inspector from making an assessment in accordance with section 919(4) or 922, as appropriate.
(a) Where as respects a chargeable period the ins