(1) In this section "assessment" includes an amended assessment.
(2) For the purposes of this Chapter, Chapter 3A and Chapter 3B of this Part, any assessment which can no longer be varied by the Appeal Commissioners on appeal or by the order of any court shall be sufficient evidence that -
(a) the income in respect of which income tax or, as the case may be, corporation tax, or
(b) the gain in respect of which capital gains tax,
is charged in the assessment arose or was received as stated in the assessment.