Section 289: Assessment to be final and conclusive.

1 Where —
a no valid objection or appeal has been lodged within the time limited by section 285 of this Act or the rules of the relevant tribunal or court, as the case may be, against an assessment as regards the amount of the hydrocarbon tax assessed,
b the amount of the tax has been agreed to under section 285 (5) of this Act, or
c the amount of the tax has been determined on objection or revision under section 285 (6) of this Act or on appeal, the assessment as made, agreed to, revised or determined on appeal, as the case may be, shall be final and conclusive for all purposes of this Act as regards the amount of such tax.

2 Where the full amount of the tax in respect of the final and conclusive assessment under subsection (1) is not paid within the appropriate period or periods prescribed in this Act, the provisions relating to the recovery of tax and to any penalty under section 292 of this Act, shall apply to the collection and recovery, subject only to the set-off of the amount of any tax repayable under any claim, made under any provision of this Act, which has been agreed to by the Service or determined on an appeal against a refusal to admit any such claim.

3 Where an assessment has become final and conclusive, any tax overpaid shall be repaid or treated as credit in favour of the assessed party.

4 Nothing in section 285 of this Act or in this Chapter shall prevent the Service from making any assessment or additional assessment to hydrocarbon tax for any accounting period which does not involve re-opening any issue on the same facts which has been determined for that accounting period, under section 285 (5) and (6) of this Act by agreement or otherwise or on appeal.