Oil Taxation Act 1975

12 (1) Where it appears to the Board—

(a) that the assessable profit charged to tax by or stated in an assessment ought to be or to have been larger or smaller; or

(b) that the allowable loss stated in an assessment or a determination of loss ought to be or to have been larger or smaller ; or

(c) that, where they made a determination that neither an assess able profit nor an allowable loss accrued in a chargeable period, they ought to have made an assessment to tax or a determination of loss for that period,

the Board may make such assessments or determinations or such amendments of assessments or determinations as may be necessary; and where the Board exercise any of their powers under this paragraph in relation to a chargeable period, they may make such adjustments in assessments or determinations for other chargeable periods as may be necessary in consequence of the exercise of those powers.

(2) Where under sub-paragraph (1) above it appears to the Board that the assessable profit for a chargeable period ought to have been larger and that the deficiency resulted from an excessive allowable loss accruing in a subsequent period having been set against the profit for that period, the Board may (notwithstanding anything in section 34 of the [1970 c. 9.] Taxes Management Act 1970 (ordinary time limit for assessments)) make a further assessment by virtue of sub-paragraph (1) above at any time not later than six years after the end of the chargeable period in which the allowable loss accrued.