(1) Subject to section 959AP, preliminary tax appropriate to a tax year for income tax purposes is due and payable on or before 31 October in the tax year.

(2)

(a) Subject to subsections (3) to (6), income tax payable by a chargeable person for a tax year shall be due and payable on or before the specified return date for the tax year whether or not an assessment is made on or by the chargeable person for the tax year on or before that date.

(b) Where an assessment to income tax for a tax year has not been made on or by a chargeable person on or before the specified return date for the tax year then the amount of tax payable that is specified in any subsequent assessment made on or by the chargeable person for that year shall be deemed to have been due and payable on or before the specified return date for the tax year.