Subject to subsections (2) and (3), a self assessment contained in a return under section 8 or 8A may be made and delivered at any time not more than 4 years after the end of the year of assessment to which it relates.
Nothing in subsection (1) prevents—
a person who has received a notice under section 8 or 8A within that period of 4 years from delivering a return including a self-assessment within the period of 3 months beginning with the date of the notice,
a person in respect of whom a determination under section 28C has been made from making a self-assessment in accordance with that section within the period allowed by subsection (5)(a) or (b) of that section.
Subsection (1) has effect subject to the following provisions of this Act and to any other provisions of the Taxes Acts allowing a longer period in any particular class of case.
This section has effect in relation to self-assessments for a year of assessment earlier than 2012-13 as if—
in subsection (1) for the words from "not more" to the end there were substituted , and"on or before 5 April 2017"
in subsection (2)(a) for the words "within that period of 4 years" there were substituted ."on or before 5 April 2017"